PIM working group S. Sami
Internet Draft
Intended status: Proposed standard November 25, 2014
Expires: May 2015
Protocol independent multicast- Next Generation (PIM-NG):
Protocol Specifications
draft-sami-pim-ng-06.txt
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Abstract
This document specifies protocol independent multicast- Next
generation or simply called PIM-NG. like PIM-SM, PIM-NG uses the
underlying unicast routing information, but unlike PIM-SM it doesn't
necessarily need to build unidirectional shared trees rooted at a
Rendezvous Point (RP) per group, due to the fact that the processes
through which a source registers with the Rendezvous Point and a host
finds the source of the multicast destination groups it needs are
done in a whole new way. So at some points PIM-NG works faster than
its predecessor. Also the new Domain concept, unique to PIM-NG, along
the RPF check method used in PIM-NG specifications provides many
features along a robust and flexible control and administration over
multicast networks.
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Table of Contents
1. Introduction...................................................5
2. Terminology....................................................5
2.1. Definitions...............................................5
3. IP Address considerations......................................9
4. PIM-NG processes..............................................10
4.1. New packet Header........................................10
4.2. Source Discovery.........................................11
4.2.1. Source register process with RP.....................12
4.2.2. Communication between client and the source.........16
4.2.3. Source specific multicast...........................26
4.2.4. Source Discovery Delay Prevention...................28
4.2.4.1. Delay prevention in Default-Mode...............29
4.2.4.2. Delay prevention in Admin-Mode.................31
4.3. Communication between PIM-NG routers.....................34
4.4. RP discovery.............................................39
4.4.1. Static RP discovery.................................40
4.4.2. Dynamic RP discovery................................41
4.4.2.1. Multicast IP addresses used....................42
4.4.2.2. Dynamic RP discovery TYPE-1....................42
4.4.2.2.1. RP introduction process...................44
4.4.2.2.2. Back up C-RP considerations...............46
4.4.2.2.3. PIM-NG clients processes in Dynamic-RP....53
4.4.2.2.3.1. New PIM-NG router/client.............54
4.4.2.3. Dynamic RP discovery type 2....................56
4.4.2.3.1. Client related concepts...................57
4.4.2.3.2. C-MAPPER concepts.........................58
4.4.2.3.2.1. Value of the A-BIT...................61
4.4.2.3.2.2. C-MAPPER preparation.................61
4.4.2.3.3. C-RP concepts.............................63
4.4.2.3.3.1. C-RP redundancy......................64
4.4.2.3.3.2. C-RP processes.......................65
4.4.2.3.3.3. Redundant C-RPs......................67
4.4.2.3.3.4. PIM-NG Anycast RP....................73
4.4.2.3.3.5. PIM-NG C-RP Mesh-Group...............74
4.4.2.3.3.6. Backup C-RP considerations...........76
4.5. C-MAPPER Redundancy in PIM-NG............................76
4.5.1. SC-MAPPER considerations............................85
4.5.2. C-MAPPER Mesh-Group.................................86
4.5.2.1. Active C-MAPPER Election.......................88
4.5.3. ANYCAST RP rules....................................89
4.5.4. Configuration process of Redundant C-MAPPERs........89
4.5.5. C-RP and Redundant C-MAPPERs........................91
4.6. Multiple multicast domains...............................92
4.6.1. Definitions and concepts............................94
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4.6.1.1. Domain.........................................94
4.6.1.2. PIM-EDGE-ROUTER (PER/PPER)....................101
4.6.1.3. Tree Root (TR)................................108
4.6.1.4. Domain-set and RPF check......................110
4.6.2. Inter-domain connectivity concepts.................114
4.6.2.1. Public Domains................................115
4.6.2.1.1. Intra-domain concepts....................115
4.6.2.1.2. Inter-domain concepts....................118
4.6.2.2. Private domains...............................121
4.6.2.2.1. Intra-Domain processes...................123
4.6.2.2.2. Inter-domain concepts....................128
4.6.3. Core-Domain implementation.........................132
4.6.4. Multiple multicast domains scenario................137
4.6.5. PIM-NG Sub-Domain..................................142
4.6.6. PIM-NG Stub-Domain.................................154
4.7. PIM-SM compatibility....................................157
4.7.1. PIM-SM compatibility and SA messages...............157
4.7.2. PIM-SM compatibility and join/prune messages.......160
4.8. Loop prevention.........................................162
4.9. DR election and PIM Assert Message......................163
5. Security Considerations......................................164
5.1. Attacks based on forged messages........................164
5.1.1. Unicast forged messages............................164
5.1.2. Forged link local messages.........................165
5.1.3. Forged multicast messages..........................165
5.2. Non-cryptographic authentication mechanisms.............166
5.3. Authentication..........................................167
5.3.1. Protecting Multicast Introduction Message..........168
5.4. Denial-Of-Service attacks...............................168
6. IANA Considerations..........................................169
6.1. PIM-NG multicast destination group addresses............169
6.2. PIM-NG packets and values of type field.................169
6.3. PIM-NG Domain numbers...................................170
7. Conclusions..................................................170
8. References...................................................170
8.1. Normative References....................................170
8.2. Informative References..................................171
9. Acknowledgments..............................................171
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1. Introduction
This document specifies a protocol for efficiently routing multicast
groups that may span wide-area (and inter-domain) internets. This
protocol is called protocol independent multicast-Next Generation or
simply put PIM-NG. The name is chosen duo to the fact that this new
protocol has some behaviors similar to PIM-SM, in parts related to
using the underlying unicast routing information base to find the
best path to reach a source and not being limited to any specific
routing protocol.
But as the overall process through which it works, in parts related
to the way a source communicates with the RP or a host finds the
desired source for a multicast group destination and receives the
desired traffic and the dynamic RP discovery methods ,are a whole new
story it is called PIM-NG or the next generation of PIM-SM[7].
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",
"MAY","ONLY" and "OPTIONAL" are to be interpreted as described in RFC
2119 [1] and indicate requirement levels for compliant PIM-NG
implementations.
Commands used in this document, MUST NOT be interpreted as the solid
commands, and are only used as an example to simplify the explanation
of the processes used by PIM-NG.
2.1. Definitions
The following terms have special significance for PIM-NG:
Candidate Rendezvous Point (C-RP):
C-RP is a router that has been configured to take the role of a
multicast information station in a PIM-NG domain. Unlike PIM-SM
specifications in RFC4601 [7], it is not used as the root of the non-
source-specific distribution tree for a multicast group. Any
multicast source will inform the RP about its existence by sending a
register message (S,G) to the RP , and RP will save the unicast
address of the source for further use in an special table. And any
host looking for the source of any desired multicast group will send
a request of (*,G) or (S,G) to the RP to receive the unicast address
of the desired multicast source.
Candidate MAPPER (C-MAPPER):
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C-MAPPER is a router in charge of introducing the existing components
of a PIM-NG multicast domain to all PIM-NG population within a
multicast domain and also is responsible for the exchange of A-
Multicast Mapping Table between different PIM-NG multicast domains.
It acts like a BSR [9] in parts related to introducing the C-RPs to
all PIM-NG routers. The difference between a C-MAPPER and a BSR is
that the C-MAPPER doesn't do the group to RP mapping. It will only
introduce the existing components such as C-RP'(s),
Client:
Client is a router that either wants to register a source, or is
looking for a source. To be more specific any none C-RP or C-MAPPER
router can be called a client. And each C-RP and C-MAPPER can act as
a client too, which is not recommended.
Tree Root (TR):
A PIM-NG-AWARE router that after being configured, MUST be introduced
to the multicast domain to become the root of each (S,G) tree. Any
client in need of receiving multicast traffic from a source will send
its join/prune messages towards the existing TR in the domain, or if
no TR is considered in the domain, directly to the existing TRs in
the core-domain.
EDGE-Client:
It is a PIM-NG client within a PIM-NG multicast domain that can act
as a boundary between downstream clients and upstream clients, to
limit the propagation of multicast introduction messages sent by C-
MAPPER'(s) or C-RP'(s). an EDGE-CLIENT can be placed at the edge of
multi-access network'(s), which are part of one unified PIM-NG
multicast domain.
PIM-EDGE-ROUTER (PER):
It is a PIM-NG aware router that connects 2 or more separate PIM-NG
multicast domains and Sub-Domains by using the underlying IGP
protocol used inside the network or a routing protocol capable of
transferring multicast traffic like MBGP.
PRIVATE-PIM-EDGE-ROUTER (PPER):
It is PIM-NG PER that is placed at the edge of a private PIM-NG
multicast domain. A PPER is also in charge of NAT operations in the
domain. As soon as the PPER is configured it MUST introduce itself to
the closest C-MAPPER in the domain.
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BORDER-PIM-ROUTER (BPR):
It is a PER or PPER which is placed between a PIM-NG multicast Domain
and a PIM-SM multicast domain, and has one or more internal
interfaces connected to the PIM-NG multicast domain and one or more
interfaces connected to the PIM-SM multicast domain. In case of using
PER as the BPR, the PER MUST introduce itself to the closest C-
MAPPER.
Second candidate Rendezvous Point (SC-RP):
SC-RP is a router configured or elected to act as the backup C-RP if
needed. And if C-RP goes offline will immediately take its place.
Second Candidate MAPPER (SC-MAPPER):
SC-MAPPER is a router configured or chosen to act as the backup C-
MAPPER if needed. And if C-MAPPER goes offline will immediately take
its place
Internal interface (II):
All interfaces of a PIM-NG router are internal interfaces by default,
and are assumed to be connected to either internal domain from a PIM-
NG-PER/PPER or PIM-NG-BPR point of view or a multi-access-network
from a PIM-NG-CLIENT point of view.
External interface (EI):
It is an interface configured as an external interface. External
interface is assumed to be connected to an external domain from a
PIM-NG-PER point of view or connected to the domain a PIM-NG-CLIENT
is a member of and thus, multicast introductions received on an
external interface won't be forwarded to internal interfaces. Also a
PIM-NG-BPR can have an external interface which is by default the
interface connected to a PIM-SM domain.
PIM-NG DOMAIN:
A domain is actually a public or private PIM-NG multicast network
including its own set of C-MAPPERs, C-RPs and clients isolated from
other domains. Clients and C-RPs inside one domain do not react to C-
MAPPER introduction messages that might be received from other
Domains. The only points of connection between 2 different domains
are the C-MAPPERs and if used PIM-EDGE-ROUTERs. Each DOMAIN can be
connected to either one or more PIM-NG-DOMAIN and if needed PIM-SM
domains or a single PIM-NG-CORE-DOMAIN.
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PIM-NG CORE-DOMAIN:
A special domain implementation of PIM-NG, which if applied gives a
hierarchical design approach, alongside a good and sound multicast
traffic flow control to the administrators of different CORE-DOMAINs.
A CORE-DOMAIN can be connected to one or more CORE-DOMAINs and one or
more PIM-NG-DOMAINs. PIM-NG-DOMAINs MUST BE connected to the outside
world or World Wide Web through a CORE-DOMAIN if they need to
advertise their multicast sources globally.
Multicast mapping table (MMT):
After a router is configured as a C-RP, a table called multicast-
mapping table is created on it. This table will then hold the
information needed to be used by clients to find a source. After a C-
RP receives a register message from a source it will put an entry for
that source in this table which indicates the unicast address of the
source plus the multicast destination group it is representing in the
format (S,G) alongside the unicast address of the client which is
sending the register message. It is done to bring compatibility with
the needs of SSM.
Abbreviated multicast mapping table (A-multicast mapping table)
(AMMT):
Is an abbreviated form of Multicast mapping table which only holds
the information regarding each source which exists in the domain and
the unicast address of that source. This table is created on C-
MAPPERs and C-RPs and is used in related processes.
PIM domain topology table (PDTT):
This table is used to store the information needed to find C-RP/RPs,
C-MAPPER, TRs and other components that may exist in a PIM-NG
multicast Domain. It holds the unicast address of such components
alongside other information needed.
Core topology table (CTT):
It is created on C-MAPPERS inside the core-domain. It only holds the
address of any existing TR'(s) inside the core domain. And is the
only PIM-NG topology table that CAN be exchanged between the PIM-NG-
CORE-DOMAIN and any existing PIM-NG-DOMAIN connected to the core
domain. Also this table is the ONLY PIM-NG topology table that CAN be
exchanged between peer C-MAPPERs in different PIM-NG-DOMAINs so that
all PIM-NG-DOMAINs will know about the TR'(s) inside the core domain.
This table MUST NOT be exchanged between PIM-NG-CORE-DOMAINs.
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Peer mapping table:
It is created on C-RPs and C-MAPPERs as soon as a C-RP or C-MAPPER
becomes peer with new C-RP or C-MAPPER.
Internal multicast source table (IMST):
This table is created on PPER'(s) and in case of private network'(s)
within a unified PIM-NG multicast domain connected to other parts of
the Network using NAT, on EDGE-CLIENTS, and helps the PPER or EDGE-
CLIENT to act on behalf of a host in search of a source by putting an
entry inside the table to keep track of the behavior of the domain.
It holds the address of the requesting client and the multicast group
requested.
Client request table (CRT):
This table is created on C-RP'(s) and holds the unicast address of
clients to which the C-RP sends a NULL-ACK in response to the clients
request to find the source for multicast group(G)along the multicast
group (G)which the client needs to find the generating source.
3. IP Address considerations
PIM-NG processes need to use 3 new multicast destination addresses
from Internetwork Control Block [2]. These addresses are going to be
used in PIM-NG processes and are needed to be assigned. For the
simplicity of explanations in this document, multicast address
239.0.1.188, 239.0.1.189 and 239.0.1.190 from the Scoped Multicast
Ranges are used as advised by IANA. But PIM-NG needs the use of
addresses from the "internetwork control block" and the use of the 3
addresses from the scoped multicast range is only for the sake of
simplicity in the process of explanation.
Also it MUST BE noted that any IP addresses, whether multicast or
unicast, used in this document from this point forward ARE ONLY used
as an example to simplify the explanation process. For example
addresses 228.8.8.8 and 229.9.9.9 are used only to simplify the
explanation process.
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4. PIM-NG processes
PIM-NG processes are related tightly to the new packet formats
defined for it. So in each section related packet formats are going
to be explained or shown.
4.1. New packet Header
The new packet'(s) format is designed and defined in the way, so it
can support the needs of PIM-NG.
The new packet header format specification for PIM-NG is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 the new packet Header
PIM-ver : is 3
As the new packet format will be used in different situations, the
new type field definitions must be explained. The new definitions are
as follows:
5 bit TYPE field to support up to 32 different functions:
Message type destination
---------------------------------------------------------------------
0- Hello Multicast to All-PIM routers
1- Register Unicast to RP and EDGE-CLIENT
2- Keep alive to RP Unicast from source to RP
3- Join/prune Multicast to ALL-PIM-ROUTERs
4- Request For Source Unicast to RP
5- Ack to Client/source Unicast from RP or EDGE-Client
To source
6- Assert Multicast to ALL-PIM routers
7- Host request to C-MAPPER Unicast to C-MAPPER
8- RP introduction Multicast to ALL-RPs
9- RP introduction Unicast to C-MAPPER
10- C-MAPPER introduction1 Multicast to ALL-PIM-NG routers
11- C-MAPPER introduction2 Multicast to ALL-MAPPERs
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12- Request-for-C-MAPPER Unicast to SC-MAPPER
13- C-MAPPER ack Unicast to Client
14- Edge Unicast to C-MAPPER
15- BPR Unicast to C-MAPPER
16- TR Unicast to C-MAPPER and
Peer-TR
17- NASN Unicast from C-RP to C-MAPPER
And Multicast from C-MAPPER to
ALL-PIM-NG routers
The above definitions will be explained, as we proceed through out
different sections of PIM-NG specifications.
4.2. Source Discovery
In the original PIM-SM specifications of the communication between a
SOURCE and RP we see that the source sends Register messages to the
RP and the RP will only accept the Register message, if any host or
hosts asked for that particular multicast group. Otherwise the RP
will send a register-stop message back to the source and the source
starts a register-suppression timer of 60 seconds. And 5 seconds
before the suppression timer expires the source sends a register-
message with its null-register bit set. Now if the RP doesn't know
any hosts asking for that specific group it will send another
register-stop. The process goes on until a host asks the RP about
that group.
Now what happens if right after the suppression timer starts by the
source a host comes up and asks for that specific source? As it is
explained in the original PIM-SM specifications, the host will have
to send its join messages to the RP until the RP hears again from the
source and this time, due to the fact that there is a host asking for
the group the RP won't send a register stop and will forward the
packet down the RPT .This process didn't seem so efficient, so some
changes has been made to the way a SOURCE communicates with the RP
alongside the new packet definitions
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4.2.1. Source register process with RP
In PIM-NG the process to initially deliver the multicast traffic to a
host asking for it, is somehow different from that of PIM-SM. It
initially starts by:
1- Source introducing itself to a router called RP(rendezvous
point)
2- RP keeps and enters the information related to the source in to
a table for further use.
3- Host asks the RP about the source of an specific group
4- Host sends a join request to the source directly
For the sake of simplicity let's consider that all the routers know
the address of C-RP. The source of the multicast traffic starts its
process by introducing itself to the C-RP, by sending Unicast-
Encapsulated register messages to it. The source does the
introduction process completely different from the original PIM-SM
specifications. In PIM-SM source introduces itself by sending a
packet containing the multicast data to be sent. But the introduction
process in PIM-NG is done through sending a register-request packet
containing only the address of the source along the multicast group
address the source represents (Figure 2). The C-RP receives the
message and by looking in its type field, it knows that it is a
Source register request message sent from a source. From here the C-
RP will act differently from what is defined in the PIM-SM
specifications.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|B| RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast destination group 1(G) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Host (server) address |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast destination group n (G) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Host (server) address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2 source register request packet
o Type: register
o Source Unicast Address: Holds the unicast address of the PIM-
NG-CLIENT sending the register message to the C-RP.
o Source HOST Address: holds the unicast address of the, server
or host in the connected LAN which is the actual generator of
the multicast data.
The C-RP looks in to the source unicast address and the Multicast
group destination address fields and puts an entry into its multicast
mapping table. The multicast mapping table consists of the multicast
group represented by a source and that source's unicast address,
along 2 timers. Figure 3 shows the multicast mapping table(MMT)
created by C-RP'(S):
+-------------------------------------------------------------------+
|Source addr(S)|Dest group (G)|Source HOST| keep alive |expiry time |
+-------------------------------------------------------------------+
| | | | | |
+-------------------------------------------------------------------+
| | | | | |
+-------------------------------------------------------------------+
Figure 3 multicast mapping table
o Source keep alive timer : the time in which RP should receive
keep alive from the source
o Source expiry time : time in which , if no keep-alive received
the entry will be deleted
Each C-RP will create another table besides the multicast-mapping
table called A-MULTICAST MAPPING TABLE(AMMT) which will be explained
later. Each new multicast destination address it enters in its MMT
will be put in the AMMT too.
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Inside the register-message, each source sends a keep-alive timer
value defaulting to 30sec to the C-RP, which later will be used by
the C-RP in the process.
Then the C-RP sends a unicast acknowledge-message(Figure 5) back to
the source, using the unicast address of the source .after receiving
the acknowledge the source proceeds with sending periodic keep-alive
messages to C-RP , to tell the C-RP that it is alive and so the C-RP
wont delete the entry related to the source from its multicast-
mapping table. For each keep-alive C-RP receives it will send an
acknowledgement. If the C-RP doesn't hear the first keep alive, it
will start to count down the expiry timer for the source which is by
default 3*keep-alive timer .if the C-RP doesn't hear from the source
in the expiry time duration it will delete the entry for that source.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP's unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast Destination Group 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast Destination Group n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4 C-RP acknowledge message
o Type : RP acknowledge to source
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Figure 5 source communication with the RP
Now let's start by explaining the process related to the
communication of the source and RP as shown in Figure 5:
1- The server behind R1 (called S1), starts sending multicast to
228.8.8.8 and R1 receives those multicasts on its connected LAN
interface.
2- R1 will try to contact the C-RP and introduce itself and the
multicast group it represents, by sending the Unicast-Encapsulated
register-request message to the address of the C-RP. C-RP receives
a PIM packet and looks at the TYPE-FIELD.
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3- After looking at the TYPE_FIELD C-RP finds out that it is a
register-request which is sent from a source. So the C-RP looks in
to the source unicast address and the Multicast group destination
address fields and writes the unicast address of the source
alongside the multicast group address it represents alongside the
keep-alive timer and the expiry timer as a new entry in its MMT.
4- RP sends acknowledge back to the SOURCE.
5- After receiving the acknowledge the source starts its keep-alive
timer ,and will send periodic keep-alive messages as long as it
wants to send traffic for the multicast group address it
represents. These keep-alive messages can be simply a register
message.
So this was the process related to the communication between a source
and the C-RP. In the next section the process related to the
communication between a host and a source, or how a host sends join
request for a multicast group address to the source will be
explained.
4.2.2. Communication between client and the source
The process through which, a host finds the source and communicates
with it in order to receive the multicast traffic, is in parts
different from that of the original PIM-SM specifications. So let's
have a flash back at the process of the original PIM-SM:
1. Host sends a join message of (*, G) to the RP, and joins the RPT
for the (*, G).
2. RP sends the join request to the source with (S,G), indicating
that a host is asking for the traffic or the RP simply forwards the
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multicast packets received from the source down RPT towards the
host.
3. Source sends the multicast packet to the RP ,and RP forwards it to
the host
4. After receiving the first couple of packets , the host sends a
join request directly to the source
5. So the host leaves the RPT and switches to SPT for (S,G)
6. Host sends a prune to the upstream router, so the RP will stop
forwarding that traffic.
This process works fine, but not as efficient and as fast as
possible. Waiting for the first couple of packets or even first
packet to be received and then switch to SPT for the (S,G) and after
that sending a prune to the upstream router ,doesn't seem so
efficient. What happens when a host sends a join for a particular
group (*, G) or (S, G) right after the RP sent a register-stop to the
source? The process seems to waste some valuable time.
So PIM-NG uses a new process to reach the source, alongside new
messages. We are going to consider that the host/hosts know about the
C-RP for now.
Let's start by assuming that a HOST behind R4(Figure 5), asks for
228.8.8.8 traffic using IGMPV2-3 .the request arrives at R4, and now
it is up to R4 to find the source and send Join message to the
source. But in order to find the source R4 knows that it will have to
ask C-RP as the information station of the Multicast domain about the
address of the source.
So R4 sends a unicast-encapsulated PIM-NG request message to the C-
RP. R4 sets the TYPE-FIELD to " Request For Source" and puts its own
unicast IP address in the "SOURCE UNICAST ADDRESS" field and puts the
multicast group address 228.8.8.8 in the format of (* , 228.8.8.8) in
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the " Multicast group destination address " field, And sends the
packet to the destination address of C-RP.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|B| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Client's unicast address(R4) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast destination group 1(G) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source of multicast group 1(*) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast destination group N (G) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source of multicast group N(*) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6 Request for source packet
. Type: Request For Source
There might be a case that there are two source HOSTs sending traffic
for the 228.8.8.8 group and the host behind R4 , asks through IGMP to
receive the traffic generated by a specific source (i.e.10.1.1.10)
.then the format of the request packet it sends will be as shown in
Figure 7.this is different from SSM multicast. As it is considered
that the CLIENT/HOST knows the address of the server or host
originating the traffic destined for group (G), but not the address
of CLIENT who is responsible for forwarding the traffic on behalf of
the server and acting as the DR.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|B| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Client's unicast address(R4) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast destination group1(G) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Host of Group 1(G)(S) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast destination group n(G) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Host of Group n(G)(S) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7 Request for Source packet format
. Type: Request For Source
C-RP receives the packet, and checks the type-field.the type-field
indicates that it is a host request to find the unicast address of a
source. So C-RP checks the Multicast group destination address field
and finds out that the host is either:
1- Looking for the unicast address of a source representing
228.8.8.8 multicast traffic (*, G).
2- Looking for the unicast address of a specific source representing
228.8.8.8 multicast traffic (*, S, G). Different from PIM-SSM.
Then the C-RP looks in to its MMT or AMMT if the network is consisted
of separate PIM-NG domains, and acts in two different ways:
1- C-RP finds an entry in its MMT which indicates that the source
exists:
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In this case, instead of forwarding the traffic towards the source
and join the SPT for (S,G), C-RP sends back the address of the source
directly toward R4 using R4's unicast address found in the "source
unicast address " field with a packet shown in Figure 8 :
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP's unicast address(R4) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GDPT |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Requested Multicast Group 1 (G) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source of group 1(G),(S) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DOMAIN-set for Group 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Requested Multicast Group n (G) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source of group n(G),(S) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DOMAIN-set for Group n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8 C-RP Acknowledge packet format
o Type: RP acknowledge to host
o DOMAIN-SET: is part of the AMMT and its use will be explained
later. It shows the domain in which a source is registered. And
also the path towards the source, so that a client can decide on
generating the join/prune message better.
o GDPT Filed: Holds the global Delay prevention timer set on C-RP
and is used to automatically synchronize this timer on all the
clients receiving a Null-ACK from C-RP.
C-RP sets the type field to "RP acknowledge to host" and puts its own
unicast IP address in the source unicast address field and fills out
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the "Multicast group destination address" field in the format of (S,
G).
One other thing that the C-RP sends back to the client is the Domain
set, which shows the domain in which the source is resided and also
the path through which the join/prune message can reach the source.
In case that the source resides in a separate domain and to be more
specific the PIM-NG network is consisted of different and separate
domains, clients will use the domain set to decide whether a
join/prune message MUST path a core domain first or MUST NOT which
the related concepts will be explained later. A Domain-Set with the
Null value in it indicates that a source is resided within a Multi-
Access Network which the related processes will be discussed in the
appropriate sections.
2- C-RP doesn't find an entry in its multicast-mapping table:
In this case C-RP answers to the host, with a packet which indicates
that the source doesn't exist now and the host must try again later.
Figure 9 shows the packet sent by RP to the host:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP's unicast address(R4) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GDPT |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Requested Multicast group 1 (G) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source of group 1(*) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Requested Multicast group n (G) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source of group n (*) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9 C-RP answer to the host in case that source doesn't exist
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o Type: RP acknowledge
R4 receives a unicast-encapsulated PIM_NG packet, and looks into the
TYPE-FIELD. The type field indicates that it is the C-RP answer to
the host request for finding the unicast address of a source. So R4
will check the source unicast address field and makes sure it was
sent from the C-RP and then looks into the Multicast group
destination address field.
R4 will act in 2 different ways, depending which one of the 2 above
conditions is meat:
1- If the entry inside the " Source of group field" is in the format
of (*, G), then R4 understands that the source doesn't exists for
now and it has to try again later .the time of resending the
request will be equal to the HELLO time or 30 seconds.
2- If the entry inside the "Source of group field" is in the format
of (S, G) then R4 will take S, and looks into its unicast routing
table to find the best way for reaching to S which is in our
example the unicast address of R1. After finding the best path to
R1, R4 sends a join/prune message to the upstream neighbor in the
best path towards the source so the join/prune messages goes hop-
by-hop until it reaches the desired destination. And depending on
whether a TR exists in the domain or not and whether any core-
domain is considered in the PIM-NG overall network, client will :
o Join the (S,G)tree in case there are no residing TRs inside the
domain
o Join the (S, G, RPT) which is assumed by PIM-NG specifications
the shortest path tree rooted at TR in case a TR exists in the
domain. Joining the (S,G,RPT) tree inside each single domain is
strongly advised due to the fact that it will reduce the
unnecessary join/prune messages being sent towards a source in
case that new clients come up later which need to receive the
same traffic.
o Join the (S, G, RPT) which is considered by PIM-NG
specifications the shortest path tree towards a source rooted
at core-domain-TR. for this tree to be formed 2 conditions
MUST exist :
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1. Core-domain MUST do exist, and any existing TR inside
the core-domain MUST be known to the PIM-NG population.
2. A source MUST be reachable by passing through the core-
domain. Which the decision is up to the client
generating the join/prune message, by checking the
DOMAIN-SET associated with a source.
This process MUST be done if the above conditions are meat,
duo to the fact that, if a PIM-NG-Core-domain exists there
will be one or more PIM-NG-DOMAINs connected to it and if one
or more new clients in other domains come up later which are
in need of receiving the same traffic, it will be waste of
time and network resources to send the new join/prune messages
towards the source. Related concepts will be explained later.
R4 MUST save the state for the join message being sent. By saving the
incoming interface for (*, G) or (S, G, TR) if it is a SSM join, and
the outgoing interface for the (S, G) or (S, G, TR).and use this for
RPF check later when receiving packets destined for (G). The related
processes are done the way described in RFC4601 [7].
The packet that is being sent by R4 to R1 as a join/prune message is
shown in Figure 10 along the new encoded source address format
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Upstream Neighbor Address (Encoded-Unicast format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Num groups | Holdtime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast Group Address 1 (Encoded-Group format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Joined Sources | Number of Pruned Sources |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Joined Source Address 1 (Encoded-Source format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tree Root address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Core Domain Tree Root Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Joined Source Address n (Encoded-Source format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tree Root address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Core Domain Tree Root Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pruned Source Address 1 (Encoded-Source format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pruned Source Address n (Encoded-Source format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast Group Address m (Encoded-Group format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Joined Sources | Number of Pruned Sources |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Joined Source Address 1 (Encoded-Source format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Joined Source Address n (Encoded-Source format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pruned Source Address 1 (Encoded-Source format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pruned Source Address n (Encoded-Source format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10Join/prune message format
o Type : join/prune
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o Tree-Root address: if any TR exists in the Domain, this field
holds the address of the TR to towards which the message MUST be
forwarded first, before being forwarded towards the source. The
concepts will be discussed later.
o Core Domain Tree-Root Address: holds the unicast address of the
TR resided in the core domain, and is used only in topologies that
contain Core-domain implementations, and incase the source is not
an internal source and MUST be reached by passing a core domain.
The related concepts will be discussed later.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Addr Family | Encoding Type | Rsrvd |S|C|R| Mask Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
Figure 11 Encoded Source Address Format
o S-BIT: only for compatibility with PIM-V1.
o R-BIT: Tree Root bit is set by the client who is sending the
join/prune message for the first time for a source in a topology
with one or more TR'(s) to join the (S, G, TR) tree. a value of 1
is set by the creator of the join/prune message to tell upstream
routers that the packet MUST be forwarded first towards the
existing TR in the domain which the address of it can be found in
the appropriate field .and a value of 0 can be set by the TR after
receiving the join/prune message and before forwarding it towards
the source. A value of 0 dictates to upstream routers that the
join/prune had reached an existing TR In the domain and from now on
MUST be forwarded towards either the source, if the source is an
internal source or there are no core domain implementations, or the
TR inside the core domain if the source is an external source that
can be reached by core domain. This bit can also be set by a PER or
by a PER/BPR in case a join/prune message is received from another
PIM-NG domain or a PIM-SM domain and must be forwarded towards any
existing TR in the domain to either reach a source inside the
domain or towards a source in other domains.
o C-BIT: Core-Domain-BIT can be set by either the client originating
a join/prune message or the TR inside the core domain. If a client
is originating a join/prune message for a source which is not an
internal source and can be reached by passing through an existing
core domain, it will set this bit to 1. A value of 1 means that the
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packet MUST be forwarded towards the TR inside the core domain
first with the unicast address that can be found in the appropriate
field. And a value of 0 can be set by the TR inside the core
domain, which dictates to upstream routers that the join/prune
message MUST be forwarded hop-by-hop towards the source from now
on. This bit can also be set by a BPR in case it receives a
join/prune message from a PIM-SM neighbor router. The related
processes and concepts will be discussed later.
Source (R1) receives the join/prune message. And joins the shortest
path tree for (G) and starts sending the multicast data destined for
(G) down the shortest path tree towards the receiver.
In order to receive packets from R1, R4 will have to send periodic
keep-alive or join messages every 30 seconds to R1. R1 receives the
join-request and will know that R4 still needs the traffic. If R1
(source) doesn't receive 2 keep-alive messages from the host (R4) it
will assume that the host doesn't exist anymore and will
automatically stop forwarding multicast traffic to the host (R4).
If R4 no longer needs to receive the traffic from R1, it will inform
R1 by sending a prune message to the upstream PIM-NG router
forwarding the traffic .this is done due to the fact that there might
be other hosts connected to the upstream routers in need of receiving
the traffic.
4.2.3. Source specific multicast
Source specific multicast (SSM) [6] can be implemented under the
following rules:
o PIM-NG routers MUST NOT send the unicast-encapsulated Request
for Source message for SSM addresses.
o PIM-NG routers MUST NOT send a register message for any packet
that is destined to an SSM address.
o If any TR exists in a PIM-NG domain, a PIM-NG router MUST join
the (S, G, RPT) rooted at the TR which is considered the
shortest path tree towards a source by PIM-NG specifications.
o ONLY incase that in a PIM-NG multicast Domain TR is implemented
and the TR and C-RP are the same components, a Client is allowed
to create the join/prune message for the SSM address and send it
towards the existing C-RP, which is also the TR.
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Figure 12 Communication between Host and Source
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4.2.4. Source Discovery Delay Prevention
One of the important factors in a multicast domain is the time
through which a client discovers or finds the source of a multicast
group (G).
Up to this point the processes through which a source registers with
C-RP and finally a client discovers the (S) for (G) by sending a
request for source message to the C-RP have been explained.
Throughout the explanations we saw that if a source is registered
,since the information regarding the source is saved in an special
table called MMT as soon as a client sends a request for source to C-
RP the C-RP will be able to send back the unicast address of (S) for
(G) in an acknowledge message to the client.
Now what happens if a client sends its request for source message to
find the (S) for (G) to the C-RP and the source (S) for (G) is not
registered yet?
As it has been explained by PIM-NG specifications, in such a case the
C-RP will send a NULL-ACK for the requested (G) back to the client
which is in the form of (*, G) and the client will have to start a 30
second timer after receiving the NULL-ACK from C-RP and send
periodical request for source messages until the source becomes
active and the C-RP responds with an acknowledge containing (S) for
(G).
Now what will happen if the (S) for (G) becomes active right after
the C-RP sends the NULL-ACK to the client?
As explained the client will have to try again in 30 seconds and send
its periodical request again to the C-RP. In this case and
considering that the (S) for (G) becomes active 1 second after the C-
RP responds to client with a NULL-ACK, the worst case scenario will
be that an unwanted 30 second delay will occur until the client sends
its request again and finds the (S) for (G).
To eliminate this delay in source discovery, PIM-NG introduces a
mechanism or process through which the C-RP will:
o Save the state of the clients to which it sends a NULL-ACK for
the requested (G).
o As soon as the (S) for (G) becomes active and registers the C-
RP will inform the clients who had been responded with a NULL-
ACK for that specific source (S).
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Through the above the C-RP will be able to inform the client as soon
as the source becomes active and the client will be able to find (S)
for (G) as fast as possible.
To do so PIM-NG specifications introduces its Source Discovery Delay
Prevention method which is divided in to 2 modes:
o Default-Mode.
o Admin-Mode.
4.2.4.1. Delay prevention in Default-Mode
This mode is activated by default as soon as a PIM-NG-Aware Router is
configured to become a C-RP and is suitable for all types of
multicast network topologies form small sized networks to large sized
networks. But it is strongly advised by PIM-NG specifications to use
this mode in small sized networks in which the number of clients are
low.
Bellow rules and specifications apply to Default-Mode:
o It is done automatically by existing C-RPs.
o It is suitable for small sized network topologies but
applicable to medium and large sized networks too.
o In this mode C-RP will save the state of clients to which a
NULL-ACK is sent in a special table called Client Request Table
(CRT). And by state PIM-NG means the unicast address of the
client alongside the multicast group (G) which the client needs
to find the associated source(S) for it and finally a timer
which defaults to 33sec (30+3).
o C-RP MUST only put an entry in CRT for the clients to which it
sends a NULL-ACK.
o For each (G) that the C-RP sends a NULL-ACK an entry MUST be
put in CRT.
o The timer which defaults to 33sec(30sec for the default
periodical client request + 3sec) is a countdown timer and
resets to 33sec ONLY when both of the bellow conditions are
true:
1- The source is not active and registered within 33seconds.
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2- C-RP receives clients periodical Request For source within
33sec which shows that the client is still interested in
finding (S) for (G).
o An entry is deleted from CRT when any of the bellow conditions
is true:
1- The source for (G) becomes active within the time period of
25 seconds or since the timer in CRT is a countdown timer 33
to 8 seconds which results in C-RP sending an Acknowledge
containing (S) for (G) to the client.
2- The source becomes active in the time period between 8 to 0
seconds and C-RP receives the periodical Request for Source
form the client and responds to client's request by an
Acknowledge of (S, G).
3- The source is not activated within the 33sec time interval
and C-RP doesn't receive the periodical Request of client for
that specific (G) in 33sec which indicates that the client is
not interested anymore in finding (S) for (G).
4- The source is activated and registered in the time interval
between 8 to 0 seconds but the C-RP doesn't receive the
periodical Request for Source from the Client which shows
that there client is not interested anymore in finding (S)
for (G).
o As long as there is an entry in CRT, for each new source (S)
that becomes active C-RP MUST check the contents of CRT and
check the (G) represented by newly activated source(S) against
the entries inside CRT and if there is a match then depending on
the time that is shown by the timer C-RP MUST act in one of the
bellow ways:
1- If the timer shows a time between 33 to 8 seconds, the C-RP
MUST immediately send its unicast-encapsulated Acknowledge
containing (S) for (G) to the client and after the timer goes
off and becomes equal to 0 delete that entry from the CRT.
2- If the timer shows a time between 8 to 0 seconds, the C-RP
MUST NOT send an Acknowledge back to the client and MUST wait
to receive the client's periodical Request for Source and
then send an Acknowledge in response to the Client's Request
and delete the entry from CRT. Note that each 30 seconds the
client who has received a NULL-ACK will send periodical
Request to C-RP and since when the timer shows 8sec we will
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have 3 seconds to the next periodical Request it will help to
reduce C-RP's work to wait for the next periodical Request,
also in case that the client is not interested anymore in
finding the (S) for (G) then at this point it will be a waste
of C-RP resources to send an Acknowledge after the timer
passes the 8sec.
o For Default-Mode to work without problem the timers on all
routers MUST be the same. Thus the C-RP sends the value of the
Timer set on it in the Null-ACK packet in the GDPT field so that
the synchronization is done automatically.
o If the default timer is changed by an administrator, the time
range in which the C-RP is to send a notification MUST be
between the higher limit and the 8 seconds. so if for instance
the time is set to 60 then C-RP MUST only send notifications
between 60 to 8 seconds.
The above being explained and since the involved processes will keep
the C-RP a little busier it is suggested to use this mode in
topologies with a low number of clients although this mode works
perfectly under any topology. Also it must be noted and considered
that due to the unique Domain concept(4.6.1.1. ) introduced by PIM-NG
which allows implementing the Sub-Domain concept(section 4.6.5) it is
possible to divide any large multicast domain to a number of smaller
domains which then makes it possible to easily use the Default-Mode
under any network topology.
4.2.4.2. Delay prevention in Admin-Mode
This mode is a suitable choice for large network topologies with many
clients which will reduce the work overhead of C-RP'(s). and is
suggested to be used in scenarios in which C-MAPPER'(s) are
considered and also the Sub-Domain concept is not considered.
Bellow rules and specifications apply to Admin-Mode:
o The Admin-Mode as the name implies needs to be activated on all
existing C-RPs by an administrator.
o For each Client's Request for Source to find the (S) for (G)
that the C-RP sends a NULL-ACK of (*, G) an entry MUST be put in
CRT.
o The entry in CRT is as explained in Default-Mode.
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o As long as there is an entry in CRT, for each new source (S)
that becomes active C-RP MUST check the contents of CRT and
check the (G) represented by newly activated source(S) against
the entries inside CRT and if there is a match then depending on
the time that is shown by the timer C-RP MUST act in one of the
bellow ways:
1- If the timer shows a time between 33 to 8 seconds and
Dynamic RP discovery type 1(4.4.2.2. ) is in use, the C-RP
which is also acting as the C-MAPPER MUST send a Multicast
Notification called New-Activated-Source-Notification(NASN)
to the entire population of PIM-NG-AWARE routers using the
destination address 239.0.1.190 which is used by this draft
for the simplicity in explaining the processes as the address
used by C-MAPPER'(s) when sending multicast introductions or
notification within the multicast domain. This notification
contains either only all the (G) for which there is an entry
in CRT or both the (G) and the unicast address of the source
(S) representing (G). both methods can be used although the
later is faster approach but less secure because it is not a
good approach to let all the clients know about the unicast
address of all the sources that are active in the domain.
2- If the timer shows a time between 33 to 8 seconds and
Dynamic RP discovery type 2(4.4.2.3. ) is in use, then the C-
RP MUST send a unicast-encapsulated New-Activated-Source-
Notification to the closest Active C-MAPPER the way it sends
its introductions. This notification contains either only all
the (G) for which there is an entry in CRT or both the (G)
and the unicast address of the source (S) representing (G).
both methods can be used although the later is faster
approach but less secure because it is not a good approach to
let all the clients know about the unicast address of all the
sources that are active in the domain. After C-MAPPER
receives the C-RP notification it will send out a multicast
notification to the entire population of PIM-NG-AWARE routers
within the domain using the destination address 239.0.1.190.
3- If the timer shows a time between 8 to 0 seconds, the C-RP
MUST NOT send the notification to the C-MAPPER and MUST wait
to receive the client's periodical Request for Source and
then send an Acknowledge in response to the Client's Request
and delete the entry from CRT. Note that each 30 seconds the
client who has received a NULL-ACK will send periodical
Request to C-RP and since when the timer shows 8sec we will
have 3 seconds to the next periodical Request it will help to
reduce C-RP's work to wait for the next periodical Request,
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also in case that the client is not interested anymore in
finding the (S) for (G) then at this point it will be a waste
of C-RP resources to send an Acknowledge after the timer
passes the 8sec.
4- In all the above conditions, after the C-RP receives the
client's request for source representing (G) for each (G)
there is an entry in CRT, the C-RP MUST delete the entry for
that (G) from the CRT after the timer goes off and is equal
to 0.
o All the clients receive the notification and those that have
received a NULL-ACK for (G) will send their queries to C-RP
again only if there is an entry for (G) they had received a
NULL-ACK for. Since considering that if the clients send their
queries immediately RP might get too busy, then each client MUST
activate a 3 second timer and after the timer goes off will send
its query. Or if the notification contains the unicast address
of the source too then clients will be able to join the SPT for
(S, G) immediately. it is possible to make modifications so that
this special notification is only readable by clients that have
received a NULL-ACK
+-----------------------------------------------------+
|Client unicast addr| Requested Group (G) |Timer |
+-----------------------------------------------------+
| | | |
+-----------------------------------------------------+
Figure 13 Client Request Table (CRT)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-MAPPER's unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Activated Group 1 (G-1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Activated Group N (G-N) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14 New-Activated-Source-Notification message format
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. Type: NASN (New-Activated-Source-Notification)
4.3. Communication between PIM-NG routers
It is important, that connected PIM-NG neighbor routers maintain a
steady state of connection. In order to do this PIM-NG routers will
send periodic HELLO messages or simply called Keep-Alive messages to
their neighbors.
This HELLO messages will be sent to the address 224.0.0.13, all PIM
routers.
What is changed is not the process of sending, rather the contents of
the hello message. A new hello packet is defined and compared to the
original PIM-SM specifications, Figure 15.
Original PIM-SM HELLO packet
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OptionType | OptionLength |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OptionValue |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OptionType | OptionLength |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OptionValue |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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PIM-NG hello packet
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|E|Z| |
|M|D|T| Reserved |
|G|C| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PIM Domain topology table |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| JOINED GROUPS TABLE |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OptionValue |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OptionType | OptionLength |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OptionValue |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15 original PIM-SM hello packet compared with the new hello
packet format
Type: HELLO
New fields are added to the new packet which in later sections their
usage will be covered:
1- RM-BIT: can be set to 1 by the sending neighbor to inform the
other neighbors about the existence of the C-MAPPER incase dynamic
methods are being used. A value of 0 indicates that the neighbor
doesn't know about any RP or C-MAPPER.
2- EDG-BIT: if set indicates to all downstream CLIENTS that a PIM
EDGE-Client exists in the network to limit the propagation of
multicast introductions sent by C-MAPPERs and C-RPs. And to
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register a multicast source the clients MUST send the register
message directly to the EDGE-CLIENT which is responsible of NAT
operations. The EDGE-CLIENT can be considered as the DR of a Multi-
Access Network which is part of one PIM-NG Multicast Domain.
Downstream routers need to look into PIM DOMAIN TOPOLOGY TABLE to
find the address of EDGE-CLIENT, if the EDGE-BIT is set.
3- ZTC-BIT: if set indicates that there has been a change in the
multicast groups the CLIENT has joined the SPT for. a PIM-NG-CLIENT
will set this bit in case there has been a change in its JOINED
GROUP TBALE and will send the table in the hello message.
4- Domain field: a 32 bit field used to announce the Domain a PIM-NG-
ROUTER is resided in to the neighbors. Only PIM-NG-ROUTERs with
matching Domains can become neighbor.
5- PIM Domain topology table: this table as described before in the
definition section, holds the information related to the C-RP'(s),
C-MAPPER'(s) and other components. What is included in this table
is actually the unicast addresses of each of the components
mentioned.
6- JOINED GROUPS TABLE: holds the list of all the multicast groups a
PIM-NG-CLIENT has joined the SPT for and is receiving the related
traffic, in the format of (S, G) or (S, S, G) which the first S
indicates the unicast address of the PIM-NG-CLIENT which is sending
the traffic to the domain and the second S indicates the address of
the host or server inside the LAN behind the client. this table
will help clients in the process of sending join messages to the
source of a multicast group in case their neighbors are already
receiving that traffic :
o the client in need of receiving multicast traffic for
(*,G)or(S,G) first looks inside this table to see if the
neighbor PIM-NG-CLIENTS has already joined the group and
receiving the traffic ,before asking the C-RP for the unicast
address of the source.
o If there is an entry in this table for the multicast group it
needs it will send a join/prune message to the neighbor for
that group.
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o If there is no entry for the multicast group it needs in this
table, it will then ask the C-RP.
o A CLINET will send the table only incase that there has been a
change in its internal JOINED GROUP TABLE , like joining the
SPT for a new group or leaving/pruning from a group .in such
cases client must inform the neighbors by setting the ZTC-BIT
in its hello message.
+-------------------------------------------------+
|Source unicast addr| Role | priority |Domain |
+-------------------------------------------------+
| | | | |
+-------------------------------------------------+
| | | | |
+-------------------------------------------------+
Figure 16 PIM domain topology table (PDTT)
o Source unicast address field: holds the unicast address, related
with either one of C-MAPPER, C-RP, SC-MAPPER, BPR or EDGE-CLIENT.
o Role: indicates that the address entry inside the source unicast
address field belongs to what component of the PIM-NG domain:
1. C-MAPPER(C-M) and SC-MAPPER(SC-M)with binary codes 1 and 2
2. C-RP and SC-RP with binary codes 3 and 4
3. A ROLE of EDGE with binary code 9, can be seen in designs, that
to reduce the propagation of multicast introduction messages, a
Client is chosen to act as the EDGE-CLIENT and will not pass any
multicast introductions received on external interfaces to
internal interfaces. In such a design the EDGE-CLIENT IS
responsible of introducing only the existing TR'(S) to its
downstream clients by sending the PIM-DOMAIN TOPOLOGY TABLE to
downstream neighbors. An EDGE-CLIENT MUST BE ONLY used in parts
of a PIM-NG multicast network where no C-MAPPER, C-RP or TR
exists. And the downstream routers MUST BE only clients. Also in
such networks a multicast source can use private IP addresses,
and such a source MUST send register messages to the existing
EDGE-CLIENT'(s). Related concepts will be explained in the
appropriate section'(S).
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4. A role of PPER (PRIVATE-PIM-EDGE-ROUTER) with binary code 8 can
be seen when a private PIM-NG domain is connected to another
domain through the use of PIM-EDGE-ROUTERs which are responsible
for the process of NETWORK ADDRESS TRANSLATION (NAT).
5. A role of BPR with binary code 10 can be seen in designs where
a PIM-NG multicast domain is connected to a PIM-SM multicast
domain. The information related to BPR is locally significant to
C-MAPPER and won't be sent to all PIM-NG routers.
6. A role of STC-MAPPER (STANDBY-C-MAPPER) with binary code 5 can
be seen in network designs with PEER-C-MAPPERs inside the same
Domain. In the case of existing Peer C-MAPPERs, C-RPs will use
the closest C-MAPPER to propagate the information associated
with existing sources inside the domain.
7. A role of TR with binary code 6 can be seen in case any TR
implementations are considered inside the domain. Please do note
that a C-MAPPER or C-RP can take the role of TR too or the TR
can be a separate and unique PIM-NG-AWARE-ROUTER inside the
domain.
8. A role of C-TR (core-TR) with binary code 7 can be seen in PIM-
NG-DOMAINs. It indicates the existence of a core-domain and the
unicast address of any existing TR inside the core domain for
further use by clients inside each domain.
o Priority: this field holds the priority related to an EDGE-CLIENT
and is used only in hello packets sent to private networks by an
edge-client. Related concepts will be discussed later.
o DOMAIN: in case separate PIM-NG multicast domains are going to be
connected to each other through the use of an EDGE router, the
Domain to which a PIM-EDGE-ROUTER is connected will be informed
inside this field. This field is usable by C-MAPPERs inside each
domain and thus won't be sent to ALL-PIM-NG-CLIENTS by C-MAPPER
when sending introductions to 239.0.1.190.
When a PIM-NG-CLIENT receives a join message from its neighbor for a
multicast group, that it is joined to and is receiving the traffic
for, it will then forward the traffic on the interface that the
neighbor is connected to and towards that neighbor.
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The definitions given by the original PIM-SM [7] are applicable to the
other fields.
4.4. RP discovery
RP discovery in general, points to the processes involved in, how a
Client finds the C-RP in the first place to send a request to and
reach the destination it wants.
In PIM-NG RP discovery is done in 3 different conditions or better to
say network topologies. Choosing the best solution depends on the
specifications of the network and will be decided by network
administrators.
Bellow the 3 different RP discovery solutions are briefly defined,
and will be explained later:
1- Static RP discovery :
The unicast address of C-RP is statically given to each PIM-NG
router through special commands.
2- Dynamic RP discovery type 1 :
Type 1 is used in networks not so big to need redundant RPs. and
also used in order to make the process of RP discovery easier and
more scalable. This type uses its own set of commands for the sake
of simplicity in explaining the processes .in this type of RP-
DISCOVERY a router is given the role of both C-MAPPER and C-RP
3- Dynamic RP discovery type 2 :
Type 2 is used in large networks with many routers, which will need
to have C-RP redundancy. Also this type is suitable for the future
needs of World Wide Web (internet). This type uses its own set of
commands for the sake of simplicity in explaining the processes. In
this type C-MAPPER and C-RP'(s) are different routers.
In the following sections the above three RP discovery methods will
be discussed.
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Also please note that any command line written in this document from
this point forward is just to provide a good sense of understanding,
and to provide simplicity in explaining the processes involved and
shall not be taken as the solid command line to be used. Also to make
the explanation process and the understanding easier some of the
processes and specifications are explained through scenarios and
examples.
4.4.1. Static RP discovery
As the name indicates, the unicast address of the C-RP which is the
IP address of a loop back interface created on RP, is set on each PIM
router so the PIM routers will be able to communicate with RP.
The process is as follows:
1- A loopback interface, typically loopback0 is created on RP and an
IP address is assigned to it.
2- The candidate RP router will know that it is the RP and will have
to use its loopback 0 by initiating the command :
by initiating this command on the router, the router understands that
it is the RP and it will have to use its loopback 0 unicast address
to communicate, or better to say it will use its loopback 0 in the "
source unicast address field " and also if it sees its loopback 0
unicast IP address as the destination of a PIM-NG packet it will have
to answer to that packet. And also it will have to bring its
interface "X, Y, Z" in to the PIM game.
3- On all the other PIM routers the bellow command is initiated :
This command tells the router that it is a client of the RP with
address of "X.Y.Z.W" .and to find any source or to be able to send
multicast traffic to any host looking for that traffic, it will have
to contact the RP through the processes explained before. And also it
will have to bring its interface "X, Y" in to the PIM game.
Since the C-MAPPER plays a significant role when it comes to
connecting different PIM-NG multicast domains and for exchanging the
information related to existing multicast sources in each domain the
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C-RP takes the role of a C-MAPPER too in the static mode. But no C-
MAPPER introduction messages will be generated by the C-RP within the
multicast domain and the additional role of C-MAPPER is only used
when exchanging information related to existing multicast sources
with other domains.
A PIM-NG specification advises that a mechanism be implemented
through which any existing components such as PPER'(s) and BPR'(s)
MUST learn about the C-MAPPER or better to say the existing C-RP
through static configuration of the C-RP unicast address.
In case any TR exists within the multicast domain or the domain is
connected to a PIM-NG core domain, PIM-NG strongly advises that the
unicast address of existing TR'(S) be introduced to each Client
through static configuration since there will be no C-MAPPER
introduction in the static RP discovery mode.
At the end PIM-NG specifications strongly advises to implement the
static RP discovery method in design plans where the multicast domain
is of small size and the domain is not connected to other domains.
And if the multicast domain whether big or small is supposed to be
connected to another domain it is strongly advised by PIM-NG
specifications to use one of the Dynamic RP discovery methods
described in the following sections.
Although in the final sections of PIM-NG specifications a new concept
will be explained which is related to connection of a Multi-Access
network which can also be considered a small sized multicast domain
to another domain or a service provider multicast domain without the
need for existing of any C-MAPPER, C-RP or TR in that Multi-Access
network which is unique to PIM-NG.
4.4.2. Dynamic RP discovery
As stated before PIM-NG uses 2 types of dynamic RP discovery methods
depending on the needs and the size of the network:
1- Dynamic discovery type 1
2- Dynamic discovery type 2
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4.4.2.1. Multicast IP addresses used
Before explaining the processes involved in PIM-NG DYNAMIC-RP-
DISCOVERY-TYPE1, there are some multicast destination group addresses
that must be defined which are used in both DYNAMIC-RP-DISCOVERY
methods:
1- Multicast group address 239.0.1.190 :
This address is reserved to be used by C-MAPPER at the time of
introducing itself to other PIM-NG routers. PIM-GN routers/clients
will listen to this multicast group address to find the C-MAPPER
and the existing C-RPS. So a new PIM-NG C-MAPPER will send its
introduction to this destination address.
2- Multicast group address 239.0.1.189: this address is required to
be used as the reserved range for the communication of RPs in order
to hold an election between RPs incase backup RPs are needed. Also
this address is used to find peers automatically in case redundant
C-RP is needed in the network.
3- Multicast group address 239.0.1.188 : this address is required to
be used as the reserved range for the communication of MAPPERs in
order to hold an election between MAPPERs incase backup MAPPERs are
needed. The usage of this range will be covered later.
Now that the addresses are defined, it is time to explain the process
through which the PIM-NG dynamic RP discovery is done and
implemented.
4.4.2.2. Dynamic RP discovery TYPE-1
There might be some network designs in which, the presence of only
one dedicated router as the RP is adequate but for administration
purposes, administrators prefer to use an automatic mechanism, so
that every PIM router will know the RP. An example of such networks
can be an enterprise or a company which uses multicast applications
such as voice and video conference often and not always. In other
words the network doesn't need to have multiple redundant RPs and
also they don't use multicast applications all the time, but for the
sake of easy administration and maintenance administrators prefer to
use the automatic mechanism.
In such a network a router will be used as the designated RP or
candidate RP (C-RP), and will introduce itself to other PIM
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routers/clients as both C-MAPPER and C-RP .and as soon as all the
clients understand about the presence of the C-MAPPER and C-RP the
rest of the process is as before.
The process is as follows:
1- A router is chosen as the C-RP. Then like the specifications of
the static RP a loopback interface is configured on it. The
loopback is better to be the loopback 0 interface.
2- The commands :
and
are initiated on the RP.
Above commands tells the router that it is both C-MAPPER and C-RP
in the network and the Dynamic discovery method used is type1 and
it should use its interface loopback "X" as the C-MAPPER and C-RP
unicast address in introductions. And it should bring its interface
"x, y,.." into the PIM-Ng game.
So router sees that it is the C-RP and the discovery protocol used
is Dynamic and the discovery method is type1, and knows that:
o It is the only RP in the network and also it must introduce
itself as the C-MAPPER.
o It is resided in domain X
o It should Send multicast introduction messages to multicast
address 239.0.1.190, out its interface "x, y" and any other
interfaces configured to be in the PIM-NG game.
o It should put the interfaces defined in the command in to
forwarding for the multicast address destinations 239.0.1.188
and 239.0.1.189.
o It should Send periodic C-MAPPER-introduction messages every 60
seconds.
o If by any means it is reloaded as soon as it comes back up, it
should send a multicast introduction to 239.0.1.190 ASAP.
3- All the other none-RP PIM-NG routers are configured as the clients
of C-MAPPER/RP.
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4- on PIM-NG none-RP routers(clients) commands :
are initiated.
above commands tells the router that it is in a PIM-NG network and
the protocol by which it can find the RP is Dynamic RP discovery
.also it understands that it should bring its interface "x ,y" and
any other interfaces dictated, in PIM-NG game.
After entering the above commands in a none-RP or a client
router'(s) the router knows that:
o it is in PIM-NG domain X
o It should use dynamic methods to find the RP .so it will wait
to receive a C-MAPPER introduction message.
o it should listen to multicast address 239.0.1.190 to hear the
C-MAPPER-introduction message to learn about the C-RP/RPs
o it should bring the interfaces mentioned in the command in PIM-
NG game
o It should put the interfaces mentioned in the command in
forward for the address 239.0.1.190 so others will hear the C-
MAPPER introduction message. Also it should put those interfaces
in to forwarding state for group addresses 239.0.1.189 and
239.0.1.188.
o If it doesn't receive the address of the C-MAPPER in the first
hello-acknowledge received from the neighbor, it should wait to
hear from the C-MAPPER.
Now that the overall process is covered, in the next section the way
RP and clients communicate will be explained and the new packet
formats will be shown.
4.4.2.2.1. RP introduction process
As soon as the router designated as the C-RP and C-MAPPER, is
configured and knows that it is the only RP in the network, it will
start the process of introducing itself as the C-MAPPER to the
network by sending the C-MAPPER-INTRODUCTION massage to the multicast
destination address 239.0.1.190 (Figure 17).
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| | | |Z| |
|M|A| G R O U P |P R I O R I T Y|T| R E S E R V E D |
| | | | | |C| |
| | | | |N| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HOLD TIME | R E S E R V E D |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-MAPPER's unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SC-MAPPER'S unicast Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PIM domain topology table |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17 C-MAPPER-INTRODUCTION massage sent to 239.0.1.190
o Type: C-MAPPER-INTRODUCTION
o RM-BIT field : if set to 1 in a C-MAPPER introduction message sent
to 239.0.1.190 , tells to all PIM-NG CLIENTS that only 1 RP exists
in the domain .so the address of the C-MAPPER is the unicast
address of C-RP . If this bit is not set to 1 then indicates to all
PIM-NG CLIENTS that in order to find existing C-RPs they should
read the contents of PDTT.
o A-BIT field: is set to 0 in this type. Its usage will be discussed
later.
o GROUP and PRIORITY fields: 8 bit fields, and are set to all zeros
when sending introduction to 239.0.1.190 .and clients won't read
the contents of these fields.
o ZTCN-BIT field : if a C-MAPPER needs to inform ALL-PIM-NG-CLIENTS
about a change it will set this bit, also if a C-MAPPER needs to
inform a change in the domain to SC-MAPPER or PEER C-MAPPERs ,it
will set this bit .use will be discussed later.
o DOMAIN: indicates the domain in which a C-MAPPER resides. It can
be used as either a security factor or as an scoping mechanism so
that clients and C-RPs inside one domain wont react to the
introductions sent from a C-MAPPER in another domain.
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o PIM Domain topology table (PDTT): when the RM-BIT is set the C-
MAPPER won't send this table in its introductions sent to
239.0.1.190, unless a TR is considered in the domain.
The Type field is set to C-MAPPER-INTRODUCTION1 so the clients
receiving the packet will know that it is an introduction message
sent from the C-MAPPER and will look directly into the "SOURCE
UNICAST ADDRESS" field. The address field contains the unicast
address of the interface loopback "X" of the C-MAPPER.and the next
field contains the address of the SC-MAPPER if any exists.
After sending the first introduction message , C-MAPPER/RP sets a
timer of 60 seconds and starts counting down to 0 ,and resends the
introduction message so all the PIM-NG routers will know that the C-
MAPPER still exists.
4.4.2.2.2. Back up C-RP considerations
If any backup C-RP is needed to be considered in such networks
explained above for the sake of high availability a mechanism for the
negotiation between the RPs and election of the candidate RP(C-RP) is
needed.
The process is as follows:
1- The addition of to the command tells the router
its group number and the PEER RP GROUP[X] tells the router that
there is another RP which it must become peer with but since the
group number of the peer is the same as its own value an
election is needed to elect the C-RP and SC-RP. The values in
front of the GROUP means that all the RPs belong to one unified
group. The usage of the GROUP will later be more clarified. and
the at the end of the command
will define each C-RP's priority in the election process :
2- If the address of the peer is not used, RPs will send multicast
introduction messages to the reserved address 239.0.1.189, so
the other RP/RPS will find each other.
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3- An election based on the highest priority configured on each C-
RP , or highest C-RP unicast address will be held between the C-
RPs
4- The candidate RP will take the responsibility of both C-MAPPER
and C-RP as explained above
5- RPs will send unicast keep-alive messages to each other every
30 second.
6- The candidate RP, C-RP, will send a copy of its multicast-
mapping table only incase that any changes occur in the domain.
And C-RP periodical introduction messages to SC-RP wont contain
any MULTICAST MAPPING table.
7- In case any changes occur C-RP will set the Z-BIT inside its
introduction message to SC-RP which indicates that a change has
occurred.
8- If more than 2 RPs are considered in a network design, an
election between none candidate RPS will be held to choose the
second best choice (SC-RP) to be the RP if the candidate RP is
dead.
9- The candidate C-RP which has the role of C-MAPPER too, will
send the unicast address of the second best candidate as SC-
MAPPER in its introduction message sent to all PIM-NG routers
every 60 second for further use by PIM-NG clients.
10- PIM-NG clients will write the address of the C-MAPPER, SC-
MAPPER and C-RP in a special table called PIM Domain Topology
Table (PDTT) for further use.
11- If SC-MAPPER/RP doesn't receive any INTRODUCTION/KEEPALIVE-
MESSAGE from the C-MAPPER/RP in 2*INTRODUCTION/KEEPALIVE-MESSAGE
plus 5 seconds timer (2*30+5) it will immediately take the place
of the C-RP and send a multicast introduction to 239.0.1.190.
12- If the SC-MAPPER/RP receives a REQUEST-FOR-C-MAPPER message
from a client asking about the existence of the C-MAPPER in 70
seconds it will react in 2 ways :
o It will immediately query the C-MAPPER/RP by sending an
introduction message and if it receives a KEEP-ALIVE message
from the C-MAPPER/RP which means the C-MAPPER/RP is still
alive then it assumes that the client which is looking for
C-MAPPER/RP is having problems .so it will return the
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address of the current C-MAPPER/RP back to the host in a
unicast C-MAPPER-INTRODUCTION (Figure 17)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| | | |Z| |
|M|A| G R O U P |P R I O R I T Y|T| R E S E R V E D |
| | | | | |C| |
| | | | |N| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-MAPPER's unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SC-MAPPER'S unicast Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PIM domain topology table |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18 SC-MAPPER/RP answers to a host REQUEST-FOR-C-MAPPER message
o Type: C-MAPPER acknowledge
o If SC-MAPPER/RP hasn't received KEEP_ALIVE messages for the
past 2*30 seconds , then it should not receive such a
message, as by now SC-MAPPER/RP must had taken the place of
C-MAPPER/RP and sent out a C-MAPPER introduction to
introduce itself. (Figure 18).
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| | | |Z| |
|M|A| G R O U P |P R I O R I T Y|T| R E S E R V E D |
| | | | |C| |
| | | | |N| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HOLD TIME | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-MAPPER's unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SC-MAPPER'S unicast Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PIM domain topology table |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19 SC-MAPPER/RP multicast introductions to all PIM-NG-CLIENTS
Type: C-MAPPER INTRODUCTION1
If clients see the address of the SC-MAPPER in the C-MAPPER unciast
address field they will assume that the current C-MAPPER is dead and
will update their tables with the new one.
13- If the previous C-MAPPER/RP gets back again then another
election will be held between RPS and the C-RP will introduce
itself.
14- All PIM-NG routers will put their interfaces inside the game
of PIM-NG into forwarding for the group address 239.0.1.189 and
239.0.1.188 and won't listen to these packets. Only will forward
them.
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Figure 20 PIM-NG network with backup RP (SC-RP)
RP introduction packet formats are shown below:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Addr length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P|Z| PRIORITY | GROUP | MESH-PRIORITY |R|reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HOLD TIME | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP'S unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sc-RP unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast MAPPING table |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| A-Multicast mapping table |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21 RP introduction message format
o Type: RP introduction
o P-BIT field (PEER): is used when a C-RP wants to become peer with
another C-RP. C-RP sets this bit to 1 and sends an introduction to
239.0.1.189. By seeing this bit set only C-RPs configured to become
peer with another C-RP from a different Group will react to the
message contents. Others will only forward.
o Z-BIT field (ZONE TOPOLOGY CHANGE NOTIFICATION): this bit is set
to 1 in case a C-RP needs to inform the SC-MAPPER C-MAPPER or
peering C-RP about any changes occurred. when this bit is set ,the
C-RP will then sends out one of the tables shown in Figure-34
depending on the fact that to whom this introduction is being sent
and in what type of domain it is resided.
o Group field: 8 bit field containing the group that the C-RP is a
member of. Helps the C-RPs to see if the packet is sent from a C-RP
they are configured to become peer with or in cases that backup C-
RP is needed. This field is set to all ZEROs when sending to a C-
MAPPER.
o Priority field: is only used when finding and communicating with
SC-RP. Otherwise set to all ZEROs.
o Mesh-priority: will be used in the process of electing the active
C-RP in a MESH-Group.
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o R-BIT: if set to 1 by a C-RP, indicates to the C-MAPPER that the
RP has the role of TR too.
o SC-RP unicast address: will be sent only when introducing to PEER-
C-RPs or C-MAPPER.and not to a back up RP.
o DOMAIN: indicates the domain the C-RP is a member of. helps the C-
RP to differ between the packets received from C-RPs inside other
domain in an special design of multiple PIM-NG multicast domains.
o Multicast MAPPING table (MMT): it is sent only when introducing to
SC-RP.and is sent in case any changes occur.
o A-Multicast MAPPING table (AMMT): this table is sent by a C-RP to
C-MAPPER in case it realizes that the domain it is resided in is
connected to another domain, or there are multiple C-MAPPERs
resided in the domain. When the C-RP receives a C-MAPPER
introduction with the A-BIT set, it starts to send this table to
the C-MAPPER. Also this table is sent by C-RP to PEER-C-RPs if any
PEER-C-RP exists.
o Hold time: is used only when introducing to C-MAPPER and indicates
the amount of time C-MAPPER will expect to hear C-RP keep-alive
message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Addr length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P|Z| PRIORITY | GROUP | MESH-PRIORITY |R|reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HOLD TIME | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP'S unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast MAPPING table |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| A-Multicast mapping table |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22 C-MAPPER/RP unicast HELLO/KEEP-ALIVE message to back up RPs
. Type: RP introduction
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4.4.2.2.3. PIM-NG clients processes in Dynamic-RP
PIM-NG router/client processes are related to the process of
forwarding special multicast traffics by default out of the
interfaces which are in the game of PIM-NG, and the processes of
finding RP and maintain connectivity with RP and PIM-NG neighbors.
The processes are as follows:
1- Each PIM-NG router using DYNAMIC-RP-DISCOVERY will put its
interfaces inside the game of PIM-NG, in to forward for the
multicast address groups 239.0.1.189, 239.0.1.190 and 239.0.1.188.
2- PIM-NG clients need to read the content of RM bit inside C-MAPPER
introduction messages to interpret the topology of the network. If
this bit is set to 1, it means that only one C-RP exists in the
network and the unicast address of the C-MAPPER inside the
introduction message is the real address of the C-RP. If this bit
is not set then clients will assume that there are possibly more
than 1 C-RP in the network and in order to find the unicast address
of C-RP or C-RPs they will have to read the contents of PIM domain
topology table, and update their local PDTT with the information
provided in this table by C-MAPPER.
3- Each PIM-NG router maintains connectivity with its neighbor PIM-NG
router through the process of sending periodic HELLO/KEEP-ALIVE
messages to its neighbor every 30 seconds.
4- If no HELLO message is received from the neighbor router in
2*HELLO time, the entry for that neighbor is erased.
5- If a PIM-NG router doesn't hear from the C-MAPPER in 70
seconds(periodic C-MAPPER introduction+10sec) it will act as
follows :
o It will send a unicast REQUEST-FOR-C-MAPPER message to the address
of the SC-MAPPER if any SC-MAPPER does exist in the network and
waits for the response from the SC-MAPPER/RP as described in the
previous section (4.4.2.2.2. ) .Figure 22 shows the format of the
packet.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Clients unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-MAPPER's unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 23 request- for-C-MAPPER packet sent to the SC-MAPPER
. Type: REQUEST-FOR-C-MAPPER
o The Client (i.e. R4) puts its own address in the client unicast
address field and the unicast address of the SC-MAPPER/RP in the
C-MAPPER unicast address field.
o If no SC-MAPPER/RP exists then it will query the neighboring PIM-
NG routers by sending a HELLO packet with the RM-BIT set to 0,
indicating that it doesn't know any C-MAPPER.
o If it doesn't receive the C-MAPPER's unicast address from the
neighbor in the first hello inside the Pim-domain-topology-table
or if the C-MAPPER address received from the neighbor PIM-NG
router is the same as its own current entry for the C-MAPPER then
it should wait to hear from the C-MAPPER.
4.4.2.2.3.1. New PIM-NG router/client
In this section, actions taken by a new PIM-NG router added to the
network using DYNAMIC-DISCOVERY without any knowledge about the C-RP
is explained:
1- Puts its interfaces defined by the related commands in to
forwarding for the multicast address groups 239.0.1.189/40/188
2- Sends HELLO message to all PIM routers address of 224.0.0.13 out
of the interfaces in the game of PIM-NG, to introduce itself to the
neighbor PIM-NG routers.
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3- If in the first received HELLO message from the neighbor it sees
the unicast address of the C-MAPPER it will use it and updates its
PMTT.
4- If no C-MAPPER address is seen in the HELLO packet received from
the upstream neighbor, it will wait to hear an introduction from
the C-MAPPER or receive it inside the next hello messages sent from
the neighbor.
5- If in the Hello message received the EDGE-BIT is set, it assumes
that it is inside a private network, and it may have to act
differently in order to register a source with the C-RP. The
related concepts will be discussed later in a separate section.
Figure 24 New client added
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4.4.2.3. Dynamic RP discovery type 2
In previous sections the processes related to the dynamic RP
discovery type 1 in which there are no needs for redundant RPs and
networks seems to be of small to medium size has been described. Now
let us consider larger networks. In larger networks (i.e. internet or
enterprises) with many multicast actions and sessions in process, the
high availability of the RPs and also load balance between RPs
through using redundant RPs becomes an important factor.
In fact hosts in different parts of a large network must be able to
find the desired source as fast as possible, if the source exists. So
as described by the original PIM-SM specifications, the network will
need redundant RPs alongside a new feature called MAPPING-AGENT or
simply PIM-NG-C-MAPPER.
C-MAPPER is in charge of introducing C-RPs to all PIM-NG routers. And
the process is in parts like the original PIM-SM RFC 4601[7], and in
parts different. Bellow the steps involved in the process of PIM-NG
is briefly described and later will be explained in details:
1- C-MAPPER introduces itself to all PIM-NG routers, so that everyone
knows about its address.
2- C-RP'(s) introduce themselves to the C-MAPPER, by sending unicast
RP introductions to the C-MAPPER's address. So they wait to receive
a C-MAPPER introduction.
3- If any TR exists in the multicast domain, it MUST introduce itself
to the closest C-MAPPER.
4- C-MAPPER will send discovery messages or introduction messages to
PIM-NG routers to inform them about the existence of the RPs so
sources can use the RP address to introduce themselves to the
nearest RP.
5- Clients or simply put all none PIM-NG C-MAPPER, RP and TR routers
will use the C-MAPPER to find RP'(s) or TR'(s).
6- Clients or simply put ALL none PIM-NG C-MAPPER, RP and TR routers
will either only-forward specific multicast address groups or
listen to them .
Figure 25 will be used as the basic topology to explain the process
related to an enterprise network with one multicast domain.
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Figure 25 network design with one multicast domain
In the following sections processes related to different components
of a PIM-NG domain will be explained.
4.4.2.3.1. Client related concepts
The processes related to a client are as described in section
4.4.2.2.3. .
Clients will choose the closest C-RP or C-MAPPER according to their
unicast routing information. And if there is a tie, they will choose
based on the highest C-RP or C-MAPPER IP address that can be found
inside the PMTT information received with the C-MAPPER introduction
message.
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4.4.2.3.2. C-MAPPER concepts
C-MAPPER is in charge of discovering C-RP'(s) and introducing them to
the population of PIM-NG routers through sending INRODUCTION-MESSAGES
to the destination address 239.0.1.190. Sending these periodic
introductions causes any existing C-RP'(s) or TR'(s) and PIM-NG
clients to learn the unicast address of the C-MAPPER and SC-MAPPER in
case any BACKUP MAPPER is considered in the network.
In the introduction message C-MAPPER will send its own unicast
address alongside the unicast address of the C-RP/RPs inside the
PMTT.
The introduction messages are sent under these circumstances:
1. Periodically as keep-alive messages so all the population knows
about the existence of the C-MAPPPER, and new routers can learn
about the C-MAPPER and the C-RP/RPs. sent to 239.0.1.190
2. Whenever it receives an introduction from a new C-RP. Sent to
239.0.1.190
3. Whenever it receives an introduction from a C-RP indicating a
change in the group addresses the C-RP represents. Sent to
239.0.1.190
4. Whenever it receives a request from a client, The C-MAPPER will
send a unicast introduction or acknowledgment in this case to
the address of the client.
5. If other MAPPERs exist in the network as backup C-MAPPERs the
MAPPERs will send introduction messages to the address group
239.0.1.188 to find each other and hold elections to elect the
C-MAPPER and SC-MAPPER (backup MAPPER) or to become PEERs.
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Message format sent to 239.0.1.190(ALL-PIM-NG-CLIENTS)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| | | |Z| |
|M|A| G R O U P |P R I O R I T Y|T| R E S E R V E D |
| | | | |C| |
| | | | |N| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HOLD TIME | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-MAPPER's unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SC-MAPPER'S unicast Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PIM domain topology table |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: MAPPER introduction1
o Group: is not used and will be set to all 0's.
o Priority: is not used and will be set to all 0's.
Message format sent to 239.0.1.188(ALL-PIM-NG-MAPPERs) and PEER-MAPPERS
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| |P| | |Z| | |
|M|A|E| G R O U P |P R I O R I T Y|T| MESH-PRIORITY |RSRVD |
| | |E| | |C| | |
| | |R| | |N| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HOLD TIME | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-MAPPER's unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SC-MAPPER'S unicast Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PIM domain topology table |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| A-MULTICAST MAPPING TABLE |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Core topology table |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 26 C-MAPPER introduction message formats
o PEER-BIT field: if set indicates that the introduction message
is meant for a PEER C-MAPPER and not for SC-MAPPERS and will be
discussed later.
o A-BIT: won't be set in this message type.
o Hold time: will be set to all 0's, when sending the
introduction to 239.0.1.188. when sending to found peers this
field holds the hold time timer that must be used for the peer.
C-MAPPER will set the type field to MAPPER introduction 1 or 2
depending on the destination group it is sending the message to. And
will put its own unicast address in the C-MAPPER unicast address
field. And also will use the SC-MAPPER unicast address field to
introduce the SC-MAPPER if any exists.
After introducing itself it will introduce any existing C-RP'(s) or
TR'(s) in the domain, by sending PMTT.
As this periodical introductions sent by C-MAPPER are used by all
PIM-NG routers to confirm the existence of the C-MAPPER and also will
be considered by all PIM-NG none-RP routers (clients) as C-RP'(s) or
any existing TR KEEP-ALIVE message , the C-MAPPER sends periodical
unicast introductions every 30 seconds to the C-RP/RPs and will
expect to hear from C-RP/RPs every 30 seconds by receiving a unicat
RP-introduction.
C-MAPPER will set the A-BIT (4.4.2.3.2.1. ) as soon as it becomes
PEER with another C-MAPPER with either different domain value or the
same domain value and different group.
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4.4.2.3.2.1. Value of the A-BIT
This bit is set by the C-MAPPER as soon as it becomes PEER with
another C-MAPPER. It indicates to the C-RPs that:
o They are in a network with more than 1 C-MAPPER which became
peers or in a network with different and separate Multicast
domains, with each domain connected to the other one through
peer C-MAPPERs.
o C-RP/RPs will have to send A-MULTICAST-MAPPING TABLE to the C-
MAPPER.
4.4.2.3.2.2. C-MAPPER preparation
The process begins by choosing a router to act as the C-MAPPER in
the PIM-NG network. For the sake of simplicity of understanding and
explaining the processes , first the processes related to a single C-
MAPPER is explained and later processes related to redundant C-
MAPPERs will be explained(4.5. ).
In a single multicast domain (Figure 25) with one C-MAPPER, the
process starts by choosing one router to act as C-MAPPER .when it is
chosen the rest is as follows:
o commands :
Are initiated on the router. This command tells the router that:
1- It is in PIM-NG DOMAIN X that uses DYNAMIC-RP-DISCOVERY
TYPE2
2- It is the C-MAPPER in the network
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3- It should bring its interfaces "x, y" and any other
interfaces configured as a PIM-NG interface in to the PIM-NG
game.
4- As no other commands are entered, it is the only MAPPER and
it is in a single multicast domain. So it MUST NOT set the A-
BIT when sending introduction messages out of its interfaces
in the game of PIM-NG.
5- It should send its introduction to multicast destination
address of 239.0.1.190 as the C-MAPPER, so all PIM-NG routers
and especially C-RP/RPs will learn its address.
6- As a PIM-NG router it should maintain connectivity with its
neighboring PIM-NG routers through sending HELLO messages out
of the interfaces defined by the command.
7- As a PIM-NG C-MAPPER it should send introduction/keep-alive
messages every 60 seconds to 239.0.1.190, so every router in
the PIM-NG network knows about its existence and the new ones
will learn its address and the C-RP/RPs address. This
periodic introduction/keep-alive messages will also act as
the introduction/keep-alive on behalf of the C-RP/RPs.
8- As soon as it receives a C-RP introduction, the C-MAPPER
will check the DOMAIN value to see if it matches its own
value and if it does the C-MAPPER will put an entry in its
PMTT alongside the multicast groups and the associated
unicast addresses it may receives from each C-RP inside the
AMMT.
9- The C-MAPPER will maintain connectivity with each C-RP by
sending periodic unicast introduction messages to the address
of each C-RP. And will expect to receive an introduction from
each C-RP in return.
10- If it doesn't receive an introduction from each C-RP for
60+10sec it will delete the entry for the RP and announces
the loss in its next introduction.
11- In case any SC-RP exists , if C-MAPPER doesn't receive a
keep alive from the C-RP for (60sec+10=70sec) , it will
automatically send an intro to the address of Sc-MAPPER.and
after receiving the first intro from Sc-MAPPER it will inform
all PIM-NG clients in an introduction message.
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Figure 27 multicast domain with one C-MAPPER
4.4.2.3.3. C-RP concepts
As explained before, the role of a C-RP in general is like an
information registry station. Any client that needs to register a
source will communicate with the C-RP and any client in need to find
a source for a multicast group (G) will have to ask the C-RP. These
parts had been covered in the first sections and we are not going to
talk about the related processes again.
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What had been explained earlier about the C-RP, was mainly related to
its processes in a domain with a small or medium size that the
presence of only one C-RP and if needed, a backup C-RP (SC-RP) could
support the needs of the network. But in larger networks beside the
high availability factor, redundancy becomes vital.
In this case there may be the need for presence of more than 1 C-RP
all working together to bring both high availability and redundancy
to the network.
4.4.2.3.3.1. C-RP redundancy
In a single domain (Figure 28) with redundant C-RPs, the main task is
for the C-RPS to find each other and also introduce themselves to all
PIM-NG clients.
Figure 28 network designs with one multicast domain
After a PIM-NG router is configured to become a C-RP and is told that
Dynamic-Discovery type 2 is in use. It needs to introduce itself to
all PIM-NG clients. To do so a PIM-NG C-RP needs to wait to learn
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about the existence of a C-MAPPER in the domain. As explained in the
previous sections this is done when a C-RP receives a C-MAPPER
introduction sent to 239.0.1.190, containing the unicast address of
the C-MAPPER. Then it will introduce itself as the C-RP to the C-
MAPPER by sending a unicast C-RP introduction message to the address
of C-MAPPER. Format of this introduction and related definitions can
be seen bellow.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Addr length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P|Z| PRIORITY | GROUP | MESH-PRIORITY |R|reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HOLD TIME | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP'S unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sc-RP unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast MAPPING table |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| A-Multicast mapping table |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 29 C-RP introduction message format
o Type : RP introduction dynamic
o Priority : set to 0
o Group : set to 0
o Hold time: Hold time is the amount of time a receiver must keep
the neighbor reachable, in seconds. If the Hold time is set to
'0xffff', the receiver of this message never times out the
neighbor. This may be used with dial-on-demand links, to avoid
keeping the link up with periodic Hello messages.
o P-BIT : set to 0
o Multicast Mapping Table : won't be sent to C-MAPPER and only to
Sc-RP
o A- Multicast Mapping Table : will be sent to C-MAPPER ,SC-RP and
peer C-RPs
4.4.2.3.3.2. C-RP processes
The processes involved are as follows:
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1- A router is chosen to become C-RP and also told that it is in a
network that a C-MAPPER exists as a separate component by
initiating a set of commands :
2- The above set of commands tells the router that it is a RP in
PIM-NG-domain(X). And it should use its LOOP-BACK "X" interface
as the RP source address when introducing itself. Also it has
to bring the interfaces "X, Y" inside the PIM-NG game and put
them into forward for 239.0.1.190, 239.0.1.189 and 239.0.1.188.
3- Because the RP discovery method used is of type2, a PIM-NG RP
waits until it hears the C-MAPPER introduction.
4- After receiving C-MAPPER introduction message first it checks
the Domain field inside the introduction message to see if the
domain value matches its own domain value it puts the source
address of the C-MAPPER into its local PIM domain topology
table.
5- The C-RP'(s) MUST check the A-BIT, to understand how should it
contact with the C-MAPPER.
6- RP sends a unicast introduction to the unicast address of C-
MAPPER and waits to receive a unicast introduction from C-
MAPPER which is interpreted as an acknowledgment from the C-
MAPPER.
7- After the acknowledgment from the C-MAPPER is received, RP
starts to sending periodical unicast introductions as keep
alive every 60 seconds to C-MAPPER in response to C-MAPPER
periodical unicast introductions.
8- If any SC-RP exists, the C-RP will also send the address of SC-
RP for further use by C-MAPPER.
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9- If any changes occur in the domain, like the registration or
deletion of a multicast group source (G) the RP will only
update its own tables since the A-BIT is set to 0.
4.4.2.3.3.3. Redundant C-RPs
Now that the processes and concepts related to each C-RP are
explained it is time to bring redundancy to the network and make C-
RPs redundant.
Considering the design shown in Figure 28, we have 2 C-RPs in our
network ,one belongs to GROUP-A and the other GROUP-B.and each one of
the C-RPs are configured up to this point to act as a C-RP and
introduce itself to the C-MAPPER. Also it should be noted that both
C-RPs MUST be inside the same DOMAIN.
In order to bring redundancy in to the network, each C-RP must be
told to become peer with a C-RP in another group, so they will be
able to exchange their entire AMMT. This way we will cover both needs
of the network which are high availability (backup C-RP) and
redundancy at the same time. But it MUST be noted that a C-RP cannot
and MUST NOT become peer with a C-RP in another domain.
The processes involved are as follows:
1- Each C-RP must be told that it belongs to a GROUP, and also
that it is peer with a C-RP from another Group. This is done by
initiating a set of commands on each RP .consider the following
set of commands are initiated on both C-RPs (Figure 28) :
2- After the above commands are initiated on C-RP-GROUP-A (C-RP-A
for simplicity) it starts a series of processes.
3- First of all it puts an entry for the new peer in a table
called PEER-LIST.
4- Sends out a multicast C-RP introduction message to all PIM-NG
C-RPs with the destination address of 239.0.1.189.
5- In the introduction message, C-RP-A sets the P-BIT to 1 which
tells to existing C-RPS that the introduction message is meant
for a C-RP that is looking for its peer. This is done duo to the
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fact that there might be SC-RPs in the network, and this bit
will make them to ignore the packet.
6- Sets the value of GROUP field to its own GROUP value.
7- Alongside its unicast address and any existing SC-RP, C-RP will
send keep-alive timer value to C-RP-B. it shows the keep-alive
timer value that C-RP-B has to set for C-RP-A.
8- One other table that is sent in this initial introduction
message is the entire AMMT of C-RP-A.
9- After receiving an introduction message from the other C-RP
which in our case is C-RP-B, C-RP-A will update its PEER MAPPING
table with information needed. And starts sending periodic
unicast introduction messages as keep-alive messages to the
unicast address of C-RP-B every 60 seconds. These periodic
introductions do not contain the MMT.
10- After the initial phase of finding C-RP-B is done, C-RP-A will
send the entire AMMT table just in case there is a change in the
domain. This change can be the registration of a new source with
C-RP-A or deletion of a source from the MMT. In such a case C-
RP-A will set the Z-BIT in its unicast introduction message.
11- In a case, that C-RP-A receives an introduction from its peer
with the Z-BIT set and containing the AMMT, it will only update
its own AMMT and won't inform the C-MAPPER about the change if
the A-BIT inside the received C-MAPPER introduction messages is
set to 1. This is duo to this fact that the change had been
informed to the C-MAPPER before by C-RP-B, and if C-RP-A is
going to inform again it will be a double introduction process
and will waste bandwidth and C-MAPPERs resources and is not a
necessary task nor recommended.
12- If C-RP-A doesn't receive an intro from the C-RP-B for 60 sec
it will send a final unicast intro to the unicast address of C-
RP-B to see if it is alive or not. If after this last unicast
introduction C-RP-A doesn't receive any introductions from C-RP-
B and there is any SC-RP-B, C-RP-A will immediately send a
unicast introduction to the address of SC-RP-B.
13- If no SC-RP-B is considered in the domain, then C-RP-A will
start sending periodic multicast introduction messages to the
address 239.0.1.189 to find its peer every 60 seconds. Until it
hears again from the C-RP-B or other C-RPs it might have became
peer with.
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The same set of actions will be done by the other C-RP (C-RP-B).
Now that the related processes are explained let's take a look at the
format of PEER-MAPPING table and PEER-LIST table which is created on
both C-MAPPER'(s) and C-RP'(s) in Figure 30.
PEER-MAPPING table
+--------------------------------------------------------------------+
|PEER ADDR|Domain|GROUP|Mesh-Group|Priority|status|keep-alive|expiry |
+--------------------------------------------------------------------+
| | | | | | | | |
+--------------------------------------------------------------------+
| | | | | | | | |
+--------------------------------------------------------------------+
o Peer unicast address: unicast address of the peer which will be
found later.
o Status: gets a value of either A (active) or S (standby) and is
used by C-MAPPERs in case more than one C-MAPPER exists.
Figure 30 PEER-MAPPING table and PEER-LIST table
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Multicast mapping table
+-------------------------------------------------------------------+
|Source addr(S)|Dest group (G)|Source HOST| keep alive |expiry time |
+-------------------------------------------------------------------+
| | | | | |
+-------------------------------------------------------------------+
| | | | | |
+-------------------------------------------------------------------+
A-Multicast mapping table
+------------------------------------------------------------------+
|Source addr|Dest group (G)|Sorce Host|Originator|DOMAIN-set|status|
+------------------------------------------------------------------+
| | | | | | |
+------------------------------------------------------------------+
| | | | | | |
+------------------------------------------------------------------+
o Status field: takes the values equal to suspend or active. If an
entry inside the AMMT has the status of suspend, it means that it
cannot be used until either it is removed or activated again but
its usage is not meant for this process and will be discussed
later. So if any entry inside this table has the status of suspend
C-RPs won't give the source address to any clients that may be
looking for the source address of a group (G) which matches that
entry.
o Domain-set: shows the domain in which a source is generated and
registered. It is called domain-set due to the fact that when
separate and different PIM-NG multicast domains are connected to
each other, a C-MAPPER inside one domain will add its domain number
to the domain value before sending the AMMT to a peer C-MAPPER in
another domain. So at the end there will be a string of domain
numbers like, 2-1-core2-core1-3-2, which will be used later. But a
C-RP only adds its domain value for any sources that is registered
with it or in a singly multicast domain design with one C-MAPPER
and multiple PEER C-RP'(s), for any source that is received from a
PEER-C-RP before sending it to another PEER-C-RP. This way the
domain-set itself can be used to RPF check.
Figure 31 AMMT compared with MMT
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+---------------------------------------+
| ORIGINATED MULTICAST GROUP 1 |
+---------------------------------------+
| ORIGINATOR UNICAST ADDRESS |
+---------------------------------------+
| MULTICAST GROUP(G) |
+---------------------------------------+
| SOURCE UNICAST ADDRESS |
+---------------------------------------+
| DOMAIN-SET |
+---------------------------------------+
| . |
+---------------------------------------+
| ORIGINATED MULTICAST GROUP N |
+---------------------------------------+
| . |
+---------------------------------------+
| DELETED MULTICAST GROUP 1 |
+---------------------------------------+
| MULTICAST GROUP(G) |
+---------------------------------------+
| SOURCE UNICAST ADDRESS |
+---------------------------------------+
| . |
+---------------------------------------+
| DELETED MULTICAST GROUP M |
+---------------------------------------+
| . |
+---------------------------------------+
| SUSPENDED MULTICAST GROUP 1 |
+---------------------------------------+
| ORIGINATOR UNICAST ADDRESS |
+---------------------------------------+
| MULTICAST GROUP(G) |
+---------------------------------------+
| SOURCE UNICAST ADDRESS |
+---------------------------------------+
| DOMAIN-SET |
+---------------------------------------+
| . |
+---------------------------------------+
| SUSPENDED MULTICAST GROUP N |
+---------------------------------------+
| . |
+---------------------------------------+
Figure 32 AMMT Format
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The above(Figure 32 ) is the real format of the A-MULTICAST MAPPING
TABLE (AMMT) being exchanged between either peering C-RP'(s) or a C-
RP and a C-MAPPER in case there are multiple PIM-NG domains or peer
C-MAPPERs in the domain ,with the bellow definitions and
specifications :
o In a single multicast domain network design which only one C-
MAPPER exists ,and multiple PEER-C-RPs are considered for
redundancy , each C-RP MUST add its domain value to the domain-
set of the received sources from a peer C-RP before sending them
to another peer C-RP. The domain-set will be used by peer C-RPs
to RPF check the received sources inside the domain. Consider
the bellow network design including 3 C-RPs all part of
multicast domain(1),in which a source registers with R1 and R1
starts to advertise the new originated source to its peers R2
and R3.R3 receives an update for (S,G) with the domain-set of D1
from R1 and another update for (S,G) with domain-set [D1,D1]
from R2.so at this point the received update from R2 fails the
RPF check because of the longer domain-set string and R3 will
only accept the received update from R1.
[R2-D1]
/ \
/ \
/ \
{(S,G),D1} / \{(S,G),D1,D1}
/ \
/ \
/ \
[R1-D1]-------------[R3-D1]
(S,G) {(S,G),D1}
o Suspended multicast group: a C-RP MUST NOT put an entry for a
suspended multicast group. This field MUST only be filled out by
a C-MAPPER or PPER which loses connectivity with its PEER-C-
MAPPER (PPER) from another domain.
Now that the processes related to bringing redundancy to the domain
by using redundant C-RPs in a single multicast domain network and
also the C-RP related processes in such a network has been covered we
are going to explain the reactions of a C-RP in a multiple domain
network and the related concepts.
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4.4.2.3.3.4. PIM-NG Anycast RP
Up to this point we have discussed the concepts related to redundant
RPs of up to 2 C-RPs in a domain. In such a multicast domain it won't
be a problem for the C-MAPPER to introduce all existing C-RPs one by
one inside the PDTT. But if the network size becomes bigger with the
need for many C-RPs to bring redundancy and high availability to the
network ,the process of introducing all existing C-RPs in the domain
by C-MAPPER to ALL-PIM-NG-ROUTERs including CLIENTS and any other C-
MAPPERs will be a waste of network resources.
So PIM-NG specifications suggest the use of ANYCAST-RP concept [11]
with bellow specifications and rules:
o Each C-RP MUST use 2 different unicast addresses. One will be
used in the processes related to introducing to existing C-
MAPPER'(s) and PEER-C-RPs. And one unicast address will be used
as the ANYCAST address. So it is better to put it this way, each
C-RP MUST use 2 interface loopbacks for its processes .one
interface with the ANYCAST address and one with the address used
for introductions.
o Clients MUST communicate with the closest C-RP.
o Existing C-MAPPERs MUST become aware of ANYCAST concept usage
in the domain alongside the ANYCAST ADDRESS in use ,by
initiating a command such as :
On any existing C-MAPPER'(s). So that C-MAPPERs will use the
configured ANYCAST address when introducing C-RPs to the domain
which will only be one entry inside the PIM DOMAIN TOPOLOGY
TABLE compared to up to 256 different C-RPs.
o If only one C-MAPPER exists in the domain or the domain is not
connected to other domains, C-RP'(s) won't need to introduce
themselves to the C-MAPPER. But C-RP'(s) MUST become peer with
each other in order to exchange the contents of AMMT with each
other to bring redundancy.
o If the A-BIT in the received C-MAPPER introduction message is
set then each C-RP will have to introduce itself to the closest
C-MAPPER and start exchanging AMMT individually with the closest
C-MAPPER.and in such case it is advised not to peer C-RPs with
each other. This is due to the fact that C-MAPPERs will inform
C-RPs about any new sources that are registered with a C-RP.
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4.4.2.3.3.5. PIM-NG C-RP Mesh-Group
Up to this point of explaining PIM-NG specifications we, have
explained the process of bringing redundancy to a PIM-NG domain by
peering C-RPs and in case the network is a large sized network ,the
usage of ANYCAST RP concept with its specifications have been
explained.
In some multicast domain designs, the needs of the network may
dictate the use of many C-RP'(s) in the domain to both bring
redundancy and high availability. ANYCAST RP concept solves a problem
regarding the introduction of C-RPs to the domain in a way that C-
MAPPER'(s) will only need to introduce one unicast address as the
address of the C-RP. But one problem remains unsolved which is
related to the fact that with ANYCAST RP, each C-RP still has to
introduce itself directly to the C-MAPPER and exchange the contents
of A-MULTICAST MAPPPING TABLE. Now if the number of existing C-RPs
goes high, the amount of data that is going to be transferred between
large number of C-RPs and C-MAPPER will waste both network and C-
MAPPER resources.
To solve the above issue PIM-NG specifications introduces the concept
of C-RP MESH-GROUP with bellow specifications:
o A PIM-NG domain can contain up to 25 C-RP Mesh-Groups. With
each group containing up to 10 C-RPs.
o A Mesh-Group priority value between [0-255] MUST be defined
on each C-RP that is going to be a member of a Mesh-Group.
This priority is different from the priority that had been
used at the time of choosing backup or SC-RP and defaults to
100. The higher the better.
o The C-RP with the highest priority in the Mesh-Group will
become the active C-RP and better to say the speaker on
behalf of the Mesh-Group.to do so an election MUST be held
between members of the Mesh-Group :
1. Each C-RP introduces itself to its peers by sending a
multicast introduction to the destination address
239.0.1.189, which contains its GROUP number, and the
priority that will be used in the election process.
2. Each C-RP receiving such introduction message will
compare the priority in the received message with its
own priority and puts an entry in its PEER-MAPPING-
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TABLE for that peer with the status of either active or
standby.
3. If the priority associated with a peer in a received
introduction is lower than the priority set on the C-
RP, then that peer will get the status of standby, and
if the associated priority of a peer is higher, that
peer gets an active status.
4. At the end of this election process, each C-RP knows
the active C-RP.
o It is advised by PIM-NG specifications that a mechanism be
implemented and used through configuration, that each member
of a Mesh-Group becomes aware about the number of members
within a Mesh-Group.
o The active C-RP in a Mesh-Group is responsible for
interacting with the closest C-MAPPER and exchanging the
AMMT which contains any sources that registers with any
members of the C-RP Mesh-Group.
o If the current active C-RP dies and doesn't have any SC-RP,
the next C-RP with the highest priority takes its place
immediately.
o Each member of the Mesh-Group MUST inform all the other
members about any changes that occurs. So for instance, if
we have 10 members in a Mesh-Group and C-RP1 receives
information regarding a new source from C-RP2, it MUST NOT
forward it to other members due to the fact that it has been
informed to other members by C-RP2.
o A C-RP can be a member of different Mesh-Groups, but such an
implementation is not advised.
o The above can be done by initiating command lines such as
the bellow command lines on each C-RP :
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PIM-NG specifications dictates that, such a command MUST
indicate the use of C-RP Mesh-Group, total number of members
in the Mesh-Group, Mesh-Group that a C-RP is a member of,
Group number of all the members of Mesh-Group that the C-RP
is supposed to become peer with and finally the priority of
the Current C-RP in the Mesh-Group.
4.4.2.3.3.6. Backup C-RP considerations
In a single PIM-NG multicast network design with redundant C-RPs
there seems that no SC-RP is needed to be considered .as each C-RP
can be used as the backup for the other one.
But in larger networks, the existence of backup RP seems necessary
and of high importance due to the fact that the high availability of
each C-RP becomes an important factor.
If any SC-RP should be considered, the processes are as explained
before with one additional table being exchanged between C-RP and SC-
RP, which is the A-MULTICAST-MAPPIN-TABLE.
4.5. C-MAPPER Redundancy in PIM-NG
Peering C-MAPPERs will bring redundancy to existing C-MAPPERs .in
large networks and special designs the redundancy between C-MAPPERs
inside the same domain might become handy.
The main use of peer C-MAPPERs is going to be felt when connecting 2
or more separate PIM-NG domains, which will be discussed later.
So for the sake of simplicity in explaining the processes involved we
are going to explain the processes in a PIM-NG network with one
multicast domain. See Figure 33.
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Figure 33 network with single multicast domain and redundant C-
MAPPERs
As you see in Figure 33 we have a single domain and redundant
MAPPERS. If you look at the picture each C-MAPPER is assigned to a
unique GROUP.
PIM-NG specifications dictate that each C-MAPPER can only communicate
with MAPPERS inside the same GROUP and domain. In other words each
MAPPER can hear the introduction of MAPPERs in other groups sent to
239.0.1.188 but won't show any reaction to it and will only forward
it, unless it is told that it can listen to the introduction of C-
MAPPER's in other groups and use the information inside the
introduction message.
The process begins by telling each C-MAPPER that it is peer with a C-
MAPPER from other groups. Consider the sample network illustrated in
Figure 33. C-MAPPER-WEST(called west for simplicity) which is in
domain 1 and is assigned to GROUP-A is told that it is peer with a C-
MAPPER in domain 1 and GROUP-B which is in this case C-MAPPER-
EAST(called east for simplicity).this must be done on both sides. As
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soon as west is told that it is peer with east a series of actions
occurs:
1- West puts an entry for east or simply GROUP-B in a special table
called PEER-MAPPING.and also an entry in the Hold Time field of the
introduction message which shows the keep-alive timer each peer
should set for the C-MAPPER-west .
+--------------------------------------------------------------------+
|PEER ADDR|Domain|GROUP|Mesh-Group|Priority|status|keep-alive|expiry |
+--------------------------------------------------------------------+
| | | | | | | | |
+--------------------------------------------------------------------+
| | | | | | | | |
+--------------------------------------------------------------------+
Figure 34 PEER-MAPPING Table
o Peer unicast address: unicast address of the peer which will be
later found.
o Status : gets a value of either A(active) or S(standby)
2- West sends a multicast introduction to the destination address of
239.0.1.188 which will be heard by all the MAPPERs .in this
introduction message the west introduces its unicast address plus
the Domain number assigned to it and the GROUP it represents and
sends its AMMT along with the PEER-LIST table. This introduction
messages will be read only by those C-MAPPERs that are supposed to
become peers with the sender, and in this case east.
3- When West becomes peer with a C-MAPPER it sets the A-BIT in its
introduction messages sent to ALL-PIM-NG-CLIENTS and All-C-RPs, so
that C-RPs start sending AMMT to C-MAPPERs.
4- If the C-MAPPERs inside the domain are forming C-MAPPER MESH-
GROUPS (4.5.2. ) then, in its introduction message sent to
239.0.1.188 to find peers from the same domain, west will send its
MESH-PRIORITY value. This priority value is going to be used in an
election process between peer C-MAPPERs forming a MESH-GROUP inside
the same domain which will be discussed later.
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5- If the C-MAPPERs are not forming a MESH-GROUP then no priority
needs to be sent.
6- West will keep sending the introduction every 30 seconds until it
receives an acknowledge or simply put introduction from east ,which
can be either a unciast introduction to west sent from east or a
multicast introduction sent from east in order to find its peers.
7- After the introduction from east is heard, and the Domain number
and group numbers are checked and verified, west keeps sending
periodical introduction messages every 60 seconds by default or
every X second equal to the time set in the KEEP-ALIVE-TIMER inside
PEER-LIST.
8- If the Mesh-Priority value of EAST is lower than its own Mesh-
Priority it means that , it is the ACTIVE-C-MAPPER and responsible
of introducing east or any other STANDBY-C-MAPPER(STC-MAPPER)
existing inside the domain to ALL-PIM-NG ROUTERs so that C-RPs will
learn the address of STANBY-C-MAPPERs to use the closest C-MAPPER.
9- Introduction messages will be sent by west under these conditions
:
o Triggered multicast introductions whenever west is told to become
peer with a new C-MAPPER.
o Periodical unicast introductions, which will act as keep-alive
messages after finding the peer. In this type of introduction no
AMMT will be exchanged.
o Triggered unicast introduction to the address of east to inform a
change in the network, like a new entry in the AMMT by setting a
flag called ZONE-TOPOLOGY-CHANGE-NOTIFICATION (ZTCN) and sending
the entire new AMMT.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| |P| | |Z| | |
|M|A|E| G R O U P |P R I O R I T Y|T| MESH-PRIORITY |RSRVD |
| | |E| | |C| | |
| | |R| | |N| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HOLD TIME | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-MAPPER's unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SC-MAPPER'S unicast Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PIM DOMAIN TOPOLOGY TABLE |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| A-MULTICAST MAPPING TABLE |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Core TOPOLOGY TABLE |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 35 introduction message format sent to ALL PIM-NG MAPPERS
224.0.1.188
o Type: MAPPER introduction
o Peer field: is set. This field will be check by other C-MAPPERs
that are looking for a peer to differentiate between
packets sent from normal MAPPERs and peer C-MAPPERs.
o Group : C-MAPPER puts its own GROUP in this field
o Domain: holds the domain number associated with the C-MAPPER
o ZTCN: ZONE-TOPOLOGY-CHANGE-NOTIFICATION. Set if any changes
occur.
A-Multicast mapping table
+------------------------------------------------------------------+
|Source addr|Dest group (G)|Sorce Host|Originator|DOMAIN-set|status|
+------------------------------------------------------------------+
| | | | | | |
+------------------------------------------------------------------+
| | | | | | |
+------------------------------------------------------------------+
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+---------------------------------------+
| ORIGINATED MULTICAST GROUP 1 |
+---------------------------------------+
| ORIGINATOR UNICAST ADDRESS |
+---------------------------------------+
| MULTICAST GROUP(G) |
+---------------------------------------+
| SOURCE UNICAST ADDRESS |
+---------------------------------------+
| DOMAIN-SET |
+---------------------------------------+
| . |
+---------------------------------------+
| ORIGINATED MULTICAST GROUP N |
+---------------------------------------+
| . |
+---------------------------------------+
| DELETED MULTICAST GROUP 1 |
+---------------------------------------+
| MULTICAST GROUP(G) |
+---------------------------------------+
| SOURCE UNICAST ADDRESS |
+---------------------------------------+
| . |
+---------------------------------------+
| DELETED MULTICAST GROUP M |
+---------------------------------------+
| . |
+---------------------------------------+
| SUSPENDED MULTICAST GROUP 1 |
+---------------------------------------+
| ORIGINATOR UNICAST ADDRESS |
+---------------------------------------+
| MULTICAST GROUP(G) |
+---------------------------------------+
| SOURCE UNICAST ADDRESS |
+---------------------------------------+
| DOMAIN-SET |
+---------------------------------------+
| . |
+---------------------------------------+
| SUSPENDED MULTICAST GROUP N |
+---------------------------------------+
| . |
+---------------------------------------+
Figure 36 A- Multicast MAPPING TABLE
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The above table (Figure 36) is the real format of A-MULTICAST MAPPING
TABLE that is exchanged between peer C-MAPPERs with bellow
definitions:
o Originator unicast address: holds the address of the C-MAPPER
that, a source is originated in its domain and it has received
the information regarding the source from a connected C-RP. It
is used by PEER-C-MAPPERs inside the same domain as a means for
RPF check of a received update regarding a source that is inside
their domain. Also the Originator address will be used when a
PIM-NG domain is going to be connected to a PIM-SM domain to
bring compatibility.
o A C-MAPPER MUST change the contents of originator unicast
address field with its own address, for sources that are
originated inside its own domain and received from a downstream
C-RP.
o A C-MAPPER MUST NOT change the contents of originator unicast
address field of sources that are received from a peer C-MAPPER
or PPER.
o Each C-MAPPER MUST add its domain number value to the domain-
set of a received source when sending the AMMT to a peer C-
MAPPER either inside the same domain or in another domain. This
domain-set is used as a means of RPF check which will be
discussed later.
o If a C-MAPPER or PPER wants to send an update to a peer in
another domain, it MUST first remove any additional domain
values equal to its domain value from the string, and then add
its domain value to the string and send it to other domains. The
additional domain values are those added by C-MAPPERs inside the
domain to be used for RPF check.
o Suspended multicast group: holds the information regarding any
multicast sources that MUST be treated as suspended .when a C-RP
receives this information it will not answer to requests from
clients for that source until the sources are again active or
deleted.
Now that west has done its part of the work, it is time to see what
are the processes related to its peer C-MAPPER-EAST.
As soon as east is told that it is peer with Group-A, it will do as
described above .also it will wait to hear a multicast introduction
destined for 239.0.1.188. When east receives such packets it will do
the following:
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1- First of all it will check the PEER field to see if it is set.
If this field is set, it means that it is sent from a C-MAPPER
that is looking for a peer or wants to introduce itself to a
peer. In our example east receives a packet destined for
239.0.1.188 .checks the PEER field .and sees that it is set by
sender.
2- East checks the Domain field to see if it is sent from inside
the domain or not.
3- Then east will check the GROUP field to see if the packet
belongs to a group it is looking for and wants to become peer
with. In this case east will see A in the GROUP field.
4- It checks its PEER-MAPPING table and sees an entry for GROUP-A
.so it understands that the packet is sent from its peer.
5- If the Mesh-Group concept is implemented, Then east checks the
Mesh-Priority value to see if the sender has a higher value or
not. And without the Mesh-Group concept EAST MUST start sending
introductions to 239.0.1.190 introducing itself to PIM-NG
population. And use the information regarding WEST to only
exchange information regarding multicast sources.
6- If the Mesh-Priority value is higher it means that it is going
to be in standby mode and only connect with existing C-RPs
through unicast introduction messages it will receive from C-
RPs. And won't send multicast introductions to 239.0.1.190 as
long as the ACTIVE C-MAPPER exists.
7- East will then look in the SOURCE-UNICAST-ADDRESS field to find
the address of the sender. And in our example east finds the
address of west, and puts the west's unicast address in its
PEER-MAPPING table alongside the associated status.
8- Now it is time for east to check the PEER-LIST table inside the
introduction message. It finds an entry for GROUP-A alongside
the associated KEEP-ALIVE timer. East then puts the associated
keep-alive timer in the right field in its PEER-MAPPING table.
9- It will read the content of the AMMT sent from west and enters
the new mappings in its own AMMT for further use.
10- It will send a unicast introduction to the unicast address of
west as an acknowledgement and also for west to learn east's
address.
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11- If any C-RP introduces itself to east , then east will have to
send the unicast address of C-RPs to west inside the PDTT so
that west will be able to introduce the existing C-RPs to ALL-
PIM-NG-CLIENTS by sending multicast introduction to 239.0.1.190.
12- East will inform C-RPs connected to it, about any changes
received inside the A-MULTICAST MAPPING table by sending unicast
introductions containing the A-MULTICAST MAPPING table to C-RPs
it knows.
Figure 37 sample illustration of the above process
The above concepts are mostly related to a design in which C-MAPPER
Mesh-Group concept is considered to reduce the amount of C-MAPPER
introduction message sent to 239.0.1.190.so without the Mesh-Group
concept:
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o each C-MAPPER starts sending introduction messages to 239.0.1.190
individually and since the C-RP'(s), RC'(s) and clients residing
in a PIM-NG multicast domain MUST communicate with the closest C-
MAPPER, then peer C-MAPPERs(WEST,EAST) MUST ONLY exchange AMMT and
do not need to exchange the information regarding C-RP'(s) or
TR'(s).
o In the case of peer C-MAPPERs without the Mesh-Group concept, if
the needs of multicasting in a domain dictates that the
information regarding existing C-RP'(s) or TR'(s) MUST be
exchanged between the peer C-MAPPERs, PIM-NG specification
strongly advices that this MUST be done through command initiation
as an optional feature.
o Duo to the fact that, in designs with more than one existing C-
MAPPER, the amount of C-MAPPER introductions destined for
239.0.1.190 will go high and will consume network resources; it is
STRONGLY advised to use the Mesh-Group concept.
4.5.1. SC-MAPPER considerations
Actions taken by C-MAPPERs and SC-MAPPER are as follows:
1- In the case of existing backup MAPPER'(s), C-MAPPER will send the
learned unicast address of the peers in its PDTT along the new
multicast groups it may learn in its introduction messages to the
SC-MAPPER so in case that the C-MAPPER crashes and dies the SC-
MAPPER will be able to immediately take its place and introduces
itself on behalf of its GROUP to the peering C-MAPPER. C-MAPPER
will inform the SC-MAPPER about any changes in the domain by
sending AMMT.
2- As explained in previous sections, if the SC-MAPPER doesn't
receive a C-MAPPER introduction for 2*30 seconds it will
immediately take its place and send a C-MAPPER introduction to the
domain. And in this case as the SC-MAPPER is aware of the existence
of PEER C-MAPPERs it will send unicast introductions to the unicast
address of peers.
3- If C-MAPPER-EAST (Figure 37) doesn't receive an introduction from
its peer for 70 seconds (default timer+10sec) it will send an
introduction to the address of SC-MAPPER-WEST .although if
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everything works accordingly by this time C-MAPPER-EAST must have
received the introduction message of SC-MAPPER-WEST.
4.5.2. C-MAPPER Mesh-Group
In a single PIM-NG multicast domain with needs for redundant C-
MAPPERs or PEER-C-MAPPERs ,a mechanism MUST be used to prevent each
single one of existing C-MAPPERs from sending multicast introduction
messages to the destination group 239.0.1.190 which will be heard by
ALL-PIM-NG-CLIENTS and PIM-NG-C-RPs. this prevention mechanism MUST
be implemented due to the fact that ,if each C-MAPPER is going to
send the mentioned multicast introduction message , the multicast
traffic created will consume lots of bandwidth and network resources.
To do so PIM-NG specifications define the concept of C-MAPPER MESH-
GROUP and ACTIVE-C-MAPPER and STANDBY-C-MAPPER (STC-MAPPER) in a way
that:
o Each Domain can have up to 25 C-MAPPER MESH-GROUPs, with each
group ONLY including up to 10 C-MAPPERs.
o Through an election between the existing C-MAPPERs, one C-
MAPPER becomes the ACTIVE C-MAPPER and all the other C-MAPPERs
become STANDBY C-MAPPERs.
o The ACTIVE C-MAPPER is in charge of introducing other C-MAPPERs
or STC-MAPPERs to ALL-PIM-NG-CLIENTS and C-RPs inside the domain
it is resided in, in case ANYCAST RP is not considered, by means
of sending multicast introduction messages to 239.0.1.190 and
sending the unicast address and role of other C-MAPPERS inside
the PIM domain topology table. So that C-RPs in different parts
of the domain will find the closest C-MAPPER and introduce to
that C-MAPPER, whether it is an ACTIVE or STANBY C-MAPPER.
o STC-MAPPERs will maintain connectivity with the active C-
MAPPER, which the related processes had been explained.
o Each STC-MAPPER will send the information related to new C-RPs
it finds to the ACTIVE-C-MAPPER by sending unicast introduction
messages and sending the PIM domain topology table inside it
which contains the information regarding the newly found C-RPs.
o Active C-MAPPER then introduces the existing C-RPs and TR'(s)
to ALL-PIM-NG-CLIENTS by sending multicast introduction messages
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to 239.0.1.190, which include PDTT. Through the above process
each CLIENT will be able to contact the closest C-RP in case it
has a source to register or it needs to find a source.
o Each C-MAPPER in a MESH-GROUP (STC-MAPPER and ACTIVE-C-MAPPER)
MUST inform other C-MAPPERs about any changes regarding the
existing multicast sources in the domain by updating its AMMT
with the information it receives from its connected C-RPs. This
way if, for instance C-MAPPER1 receives an update from C-
MAPPER2, it will not need to send it to C-MAPPER3 as it has been
done by C-MAPPER2.
o C-MAPPERs, both ACTIVE and PASSIVE, MUST then inform their
connected or downstream C-RPs about any changes regarding the
existing multicast sources by sending the AMMT. This way ALL-
PIM-NG C-RPs in different parts of the network will have enough
information about the domain to answer the requests of clients
in need of finding a source. This process will eliminate the
need for PEER C-RPs.
o If the design of multicast domain, dictates to form more than
one C-MAPPER Mesh-Group, PIM-NG specifications STRONGLY advises
to place a boundary between different Mesh-Group areas by simply
putting PER'(s) where ever needed. This will limit the
propagation of C-MAPPER introduction messages sent by ACTIVE-C-
MAPPER in each Mesh-Group area to other areas and will reduce
the network resources consumption by unwanted multicast traffic.
o If no boundary is considered between different areas,
components of the PIM-NG domain such as C-RP, Client, and ETC,
MUST react to the introduction message of the closest ACTIVE C-
MAPPER according to the contents of the SOURCE UNICAST ADDRESS
field of the introduction message and the information inside the
unicast routing table. The only issue within the domain MUST BE
ONLY the consumption of network resources by unnecessary
multicast traffic related to multiple ACTIVE C-MAPPER
introduction messages.
o In the case of implementing more than one Mesh-Group, each area
separated from other areas by PER'(s) will act normally, and
existing components such as C-RP'(s), Clients and other
components will respond to the introduction messages received
from the active C-MAPPER in the area.
o If a PIM-NG domain is consisted of more than one C-MAPPER Mesh-
Group and separated in to different areas, PIM-NG specification
STRONGLY advises to peer 2 C-MAPPERs from each Mesh-Group with
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each other using the static methods so that the information
related to multicast sources in each area reaches other areas.
Using the static method of connecting 2 different Mesh-Group
will eliminate the need for the C-MAPPER introduction messages
sent to 239.0.1.188 to find other C-MAPPERs, to be forwarded by
PER'(s) between areas.
o If a C-MAPPER in a Mesh-Group is becoming peer with a C-MAPPER
in another Group, depending on the needs of multicasting in the
domain, it may need to advertise the information regarding the
existing C-RP'(s) and TR'(s) too, so in case anything happens to
C-RP'(s) or TR'(s) in one area, the network stays stable and
converges automatically. PIM-NG specifications advise to do this
through command initiation on C-MAPPERs as an optional feature.
4.5.2.1. Active C-MAPPER Election
The election process starts as soon as a c-MAPPER inside a domain
becomes aware that it is part of a MESH-GROUP and is peer with a C-
MAPPER inside the same domain but with a different group. The related
processes are explained bellow:
1- As soon as each C-MAPPER becomes aware that it is peer with
another C-MAPPER in a MESH-GROUP in the same domain but with a
different group, it starts the process of sending multicast
introduction messages to ALL-PIM-NG C-MAPPERs destination
address of 239.0.1.188.
2- Each C-MAPPER will set the PEER-BIT, so that incase there are
any SC-MAPPERs inside the network, they won't read the contents
of the message.
3- Each C-MAPPER sends its domain number, group number, alongside
the priority to be used in the process of election.
4- As soon as each C-MAPPER receives an introduction from its peer
C-MAPPER, it will compare the Mesh-Priority value inside the
introduction message with its own Mesh-Priority value.
5- If the received priority value is higher than its own priority
value then, it will put an entry for the peering C-MAPPER inside
its PEER-MAPPING table with the status of ACTIVE. And by this
time the C-MAPPER understands that it is the STC-MAPPER and must
act as one.
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6- If the received priority value is lower than its own priority
value then an entry will be put in the PEER-MAPPING table with
the status of STANDBY. And by this time the C-MAPPER knows that
it is the active C-MAPPER and should act as an ACTIVE-C-MAPPER.
7- In case there is more than 2 C-MAPPERs inside the domain, and
thus each C-MAPPER is configured to become peer with more than 1
C-MAPPER from its own domain, then each C-MAPPER must do the
above processes until it finds all of its peers and comes to a
conclusion that who is the ACTIVE-C-MAPPER inside MESH-GROUP in
the domain.
8- It is strongly advised by PIM-NG specification that a mechanism
be implemented through configuration that informs each C-MAPPER
about the total number of C-MAPPERs that are members of a Mesh-
Group.
9- By this time each C-MAPPER knows that which C-MAPPER is the
active one .so without doing much more process, each C-MAPPER
will silently accept its role and starts the related process.
Through the above processes existing C-MAPPERs in a domain can decide
who is the ACTIVE-C-MAPPER and the rest of them will be STC-MAPPERs.
4.5.3. ANYCAST RP rules
When ANYCAST RP is in use, and more than one C-MAPPER is implemented
in the domain, a C-MAPPER MUST NOT send the information regarding any
new C-RP it finds through the introduction processes, to its peers.
This is due to the fact that from the CLIENTS point of view ALL-C-RPs
has the same unicast address.
Each C-MAPPER MUST maintains connectivity with each C-RP it finds.
4.5.4. Configuration process of Redundant C-MAPPERs
With explanations in previous sections the process is straight
forward also refer to Figure 37 if needed:
1- Each component residing inside a domain is supposed to have a
domain number. So it is assumed that up to this point ALL-PIM-NG
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routers inside a domain has been configured with a command which
indicates the domain a CLIENT , RP and MAPPER resides in :
The concepts related to DOMAIN are explained in section 4.6.1.1. .
2- Each C-MAPPER needs to be assigned a GROUP number :
The above commands tells the C-MAPPER that it belongs to a
specific GROUP, which in our illustrated example will be
GROUP-A(west) and GROUP-B(east).please keep in mind that the
group value is a number between 1 to 255
3- Each C-MAPPER needs to know its peer GROUP and if needed the
address of the peer:
Or in case of a mesh group
THE above command lines dictates to the C-MAPPER that it must become
peer with a C-MAPPER from DOMAIN X and GROUP[0-255] ,which in our
example will be GROUP-B for west and GROUP-A from east. And also it
should use the configured priority value to be used in ACTIVE-C-
MAPPER election.
Or in case of implementing the Mesh-Group concept dictates the Mesh-
Group Number, total number of Mesh-Group members, group number of the
peer or the unicast address of the peer C-MAPPER and finally the
priority used in the Active C-MAPPER election.
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4- In case the unicast address of the peering C-MAPPER is used the
router will send unicast introduction messages to its peer.
Although not advised because of the dynamic nature of this process,
and especially when there are backup peers in each group, but it is
a way to do it.
4.5.5. C-RP and Redundant C-MAPPERs
In such network designs with redundant C-MAPPERs, Active C-MAPPER
informs the C-RPs about the existing C-MAPPERs inside the domain by
sending multicast introduction messages to ALL-PIM-NG-CLIENTS
destination address 239.0.1.190.
Also as described before as soon as a C-MAPPER becomes peer with
another C-MAPPER it will set the A-BIT when sending introduction
messages to either ALL-PIM-NG-CLIENTs (239.0.1.190) or unicast
address of a C-RP.
The above processes dictate to the existing C-RPs that they MUST:
o Find the closest C-MAPPER based on the unicast address of the
C-MAPPER and the information inside the unicast routing
information base.
o Introduce to the closest C-MAPPER.
o If any changes occur inside the domain like, the registration
of a new source or deletion of a new source, each C-RP must
inform the C-MAPPER by sending the AMMT to the C-MAPPER. This
way other C-RPs inside the domain will receive the information
regarding a new source registration inside the network from
their closest C-MAPPER which they had introduced themselves to
it.
o If a C-RP receives a request from a CLIENT for a source, C-RP
MUST send the Domain-set associated with a source to the
client, so that the client knows that where the source is
generated and use the DOMAIN-SET later when sending a join
request to the source.
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4.6. Multiple multicast domains
Throughout the specifications of PIM-NG up to this point the concepts
and processes that occur in a single PIM-NG multicast domain have
been explained.
But in large sized networks such as an enterprise network or the
World Wide Web (WWW) itself, the need for using multiple multicast
domains instead of a single multicast domain is needed to be
considered.
Examples of such cases can be:
o Enterprise networks ,which the needs of the network dictates to
divide the multicast domain in to 2 or more separate domains
to have a better control over the propagation of the multicast
traffic.
o Enterprises or companies, with buildings and networks in
different places. With each network or building connected by
means of GRE-TUNNELs or MP-BGP to carry multicast traffic.
o The internet as the biggest network of all, which is divided to
different multicast domains, each connected to the other ones
by different methods like MP-BGP as the carrier protocol of
multicast traffic.
connecting 2 or more PIM-NG multicast domains to exchange the
information regarding the multicast sources originated in each
domain, is done through making 2 or more C-MAPPERs from one domain
peer with one or more C-MAPPER'(s) in the other domain. The C-MAPPERs
then will start to exchange their AMMT'(s) with each other through
sending unicast-encapsulated introduction messages to each other. And
because of the bellow facts:
o the propagation of multicast introduction messages of one
domain in to other domains is not desired.
o a PIM-NG domain may be 1 or more Autonomous Systems away.
o There may be a transitory AS between 2 PIM-NG domains, which
only provides the connectivity in terms of forwarding
multicast traffic destined for group (G) or join/prune
messages. Such a scenario can be seen in designs where 2 PIM-
NG domains are either connected through an ISP or a PIM-SM
network.
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o There might be one or more AS'(s) or networks between 2 PIM-NG
domains, that must not receive the information regarding some
of the sources that are being originated, or must not receive
them at all. But their network infrastructure is needed to
forward join/prune messages and multicast traffics.
C-MAPPERs MUST NOT use the automated mechanisms described up to this
point to become peers and MUST use the unicast address of their
desired peers in other domains.
Also PIM-NG uses a unique method to RPF check the received
information regarding multicast sources which provides the existence
of transitory Ass unlike the RPF check method used in PIM-SM and MSDP
which has some limitations in this part.
So PIM-NG specifications uses some rules, processes and definitions
specific to PIM-NG to connect different PIM-NG domains or a network
of PIM-NG domains with a network of PIM-SM domains, which are
explained in the following sections.
Figure 38 network with 2 PIM-NG multicast domains
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4.6.1. Definitions and concepts
In the following sections different features and rules that are used
when connecting multiple PIM-NG multicast domains, and related
definitions and concepts are explained.
4.6.1.1. Domain
PIM-NG introduces the concept of domain in a way that each domain is
distinguished from the other domains by the domain number or value.
Each domain has its separate set of CLIENTS, C-RPs, TRs and C-
MAPPERs.
PIM-NG uses a 32 bit domain field to support future needs of
multicasting and classifies the range in to 4 groups which are
explained bellow. But PIM-NG specifications suggest to different
methods of domain number assignment which both of them classifies the
range in to 4 groups:
1- This method is unique to PIM-NG specifications and we STRONGLY
advise the use of this method which will need the domain numbers
to be either globally unique and assigned by IANA or locally
unique and assigned by either the RIRs or an entity or enterprise
with a unique PIM-NG-CORE-DOMAIN number:
o Domain range [1-9900] as PIM-NG-DOMAIN.
o Domain range [9901-9999] as PIM-NG-DOMAIN for private,
experimental and documentation use.
o DOMAIN range [10000-4294000000] as PIM-NG-Core-DOMAIN.
o Domain range [4294000001-4294967293] as PIM-NG-Core-DOMAIN for
private, experimental and documentation use.
o Domain numbers 0 and 4294967294 are reserved.
2- This method won't need any assignment by IANA or any RIR, since a
domain number will be the same as the globally unique autonomous
system number (AS number) assigned by IANA to be used as PIM-NG-
CORE-DOMAIN numbers, and PIM-NG-DOMAIN numbers will be chosen from
the private ranges. But this method is only introduced to make the
domain number assignment easier and is not the advised method:
o Domain range [1-64511] and [64536-4200000000] as PIM-NG-CORE-
DOMAIN numbers which due to the fact the numbers are assigned
by IANA as AS numbers, they are globally unique.
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o Domain range [64512-65512] as PIM-NG-DOMAIN numbers. This range
needs to be locally unique from the RIR-CORE-DOMAIN point of
view or the CORE-DOMAIN of an entity or enterprise.
o DOMAIN range [65513-65535] as PIM-NG-DOMAIN numbers for
private, experimental and documentation use.
o Domain range [4200000001-4294967293] as PIM-NG-Core-DOMAIN for
private, experimental and documentation use.
o Domain numbers 0 and 4294967294 are reserved.
Now that the domain number classifications are explained, we are
going to explain the rules and specifications that apply to the above
classifications.
The bellow specifications and rules apply to ALL-PIM-NG domains:
1- All clients inside a domain MUST have the same domain number.
2- All C-RPs inside a domain MUST have the same domain number, as
the clients.
3- All C-MAPPERs inside a domain MUST have the same domain number
as the CLIENTs.
4- All TRs inside a domain MUST have the same domain number as the
C-MAPPER.
5- Clients MUST only respond to or accept HELLO messages from a
neighbor with matching domain number.
6- Clients MUST only accept and respond to C-MAPPER introduction
messages sent to 239.0.1.190, which has a matching domain
number.
7- C-RPs MUST only accept and respond to C-MAPPER introduction
messages sent to 239.0.1.190 or unicast C-MAPPER introduction
messages with matching domain number.
8- C-RPs can only become peer with C-RPs inside the same domain,
so a C-RP MUST NOT accept or respond to the C-RP introduction
message sent to 239.0.1.189 from other domains.
9- C-MAPPERs can become peer with C-MAPPERs from the same domain
or from other domains.
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10- C-MAPPERs MUST BE the only means to exchange the information
regarding the existing sources in each domain by exchanging A-
MULTICAST MAPPING TABLES.
11- IF a DOMAIN is needed to be connected to another domain it MUST
be connected through one or more PIM-EDGE-ROUTERs (PER/PPER) to
prevent the propagation of unnecessary multicast introduction
traffic in each domain. In case an enterprise needs to divide
its multicast domain in to 2 or more sub-domains, it is strongly
advised to use PERs to prevent the fellow of unnecessary
multicast introduction traffic of one domain to other domains.
12- C-MAPPER'(s) MUST introduce all existing C-RPs and TRs they
find inside the domain to ALL-PIM-NG-ROUTERs inside the domain
(230.0.1.190).
13- C-MAPPERs MUST remove any private DOMAIN, private CORE-DOMAIN
or sub-domain number before advertising any multicast source
globally or to be more specific to a peer C-MAPPER in another
domain.
The bellow specifications and rules apply to PIM-NG-DOMAINs:
1- PIM-NG-DOMAIN number values MUST be unique from the connected
PIM-NG-CORE-DOMAIN point of view .so the values MUST be assigned
by a local organization or Regional Internet Registry who has a
globally unique PIM-NG-CORE-DOMAIN number, in case the
enterprise doesn't have a PIM-NG-CORE-DOMAIN number which is
globally unique.
2- A PIM-NG-DOMAIN can be either a public network or a private
network which is connected to the public network by using the
NETWORK ADDRESS TRANSLATION. And by private PIM-NG specification
means that all the components of the PIM-NG domain such as C-
MAPPERs and even sources can use private unicast addresses.
3- An enterprise can use any PIM-NG-DOMAIN number from the
classified range freely as long as it doesn't need to advertise
its multicast sources globally and by advertise from now on we
mean sending any existing multicast sources to a peer C-MAPPER
inside a PIM-NG-CORE-DOMAIN with a globally unique domain number
by sending A-MULTICAST-MAPPING-TABLE inside the unicast-
encapsulated C-MAPPER introduction message.
4- If an enterprise needs to advertise its multicast sources
globally but does not wish to or doesn't need to apply to get a
globally unique PIM-NG-CORE-DOMAIN number , it MUST apply to get
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a unique PIM-NG-DOMAIN number from the Regional Internet
Registry and advertise its multicast sources through the
Regional Internet Registry's PIM-NG-CORE-DOMAIN.
5- If an enterprise with more than one PIM-NG-DOMAINs all
connected through an Internet Service Provider(ISP) backbone
,doesn't need to advertise its multicast sources globally and
only needs to use them internally , it doesn't not need to
become connected to the ISP by making one or more C-MAPPERs peer
with a C-MAPPER inside the ISP backbone ,due to the fact that
PIM-NG specifications uses its special unicast introduction
method to make C-MAPPERs in different domains peer alongside its
RPF check method unique to PIM-NG ,and doesn't use MSDP.
6- If a multicast source inside a PIM-NG-DOMAIN needs to be
globally accessible it MUST be first advertised to a peer C-
MAPPER inside an existing PIM-NG-CORE-DOMAIN.
7- If an enterprise needs to divide its multicast domain into 2 or
more multicast domains, without the need of applying to get more
than one locally unique PIM-NG-DOMAIN number from the Regional
Internet Registry, it can do so by dividing its multicast domain
into 2 or more domains as sub-domains of the main domain which
is assigned by the Regional Internet Registry. The related
concepts will be discussed later.
8- A PIM-NG-DOMAIN can be connected to a PIM-NG-CORE-DOMAIN
through another PIM-NG-DOMAIN or even an existing PIM-SM domain
and does not need to be directly connected to send join/prune
messages or receive traffic for a multicast destination group.
But in order to advertise its multicast sources globally it MUST
be connected to either the neighbor PIM-NG-DOMAIN which is
connected to a core domain or directly to the PIM-NG-CORE-DOMAIN
and by connected PIM-NG specifications dictates that at least
ONE C-MAPPER inside the PIM-NG-DOMAIN MUST be a peer with either
a C-MAPPER inside the neighbor domain or inside the core domain.
9- Normal domains can have one or more Tree-Roots(TR).if TR exists
in a domain the join/prune messages MUST first be forwarded
towards the existing TR, and then towards the source.
10- If the network is consisted of PIM-NG-CORE-DOMAINs (CD) and a
client is in need of sending join/prune towards a source which
can be reached through an existing PIM-NG-CORE-DOMAIN, and TR or
TRs are considered in each PIM-NG-DOMAIN, each client MUST first
send its join request for a source towards the TR residing
inside its domain and then after the join/prune message reached
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the local TR it MUST be forwarded towards the TR inside the PIM-
NG-CORE-DOMAIN . So all clients residing inside PIM-NG-DOMAIN
MUST have knowledge about the existence of the CORE-DOMAIN TR or
TRs.
11- When a PER/PPER receives join/prune message on an external
interface which is connected to either another domain or public
networks, destined for a source inside its domain or a TR inside
an existing PIM-NG-CORE-DOMAIN or a source in another domain it
MUST forward it first toward the closest TR inside its own
domain by setting the R-BIT inside the source address field of
the received join/prune and putting the address of the closest
TR in the appropriate field and then the TR will forward the
traffic towards the source or existing TR inside the PIM-NG-
CORE-DOMAIN if it is dictated inside the join/prune message.
This process will eliminate unnecessary join message traffic
towards a source in case many CLIENTS will need the same
specific traffic. Or a new CLIENT may ask to receive the same
traffic.
12- A C-MAPPER MUST add its domain number to the domain-set of any
received multicast sources received from PEER-C-MAPPERs in other
domains before advertising them to other PEER-C-MAPPERs in other
domains.
13- A C-MAPPER inside a PIM-NG-DOMAIN MUST add its domain number
to the domain-set of any received multicast sources from other
domains when advertising to a PEER-C-MAPPER inside the same
domain. These additional prepended domain values will be use by
C-MAPPERs inside the domain for RPF check.
14- A C-MAPPER inside a PIM-NG-DOMAIN MUST add its domain number
to the domain-set of any received multicast sources from peer C-
MAPPERs inside the domain to a PEER-C-MAPPER inside the same
domain. These additional prepended domain values will be use by
C-MAPPERs inside the domain for RPF check.
15- If a C-MAPPER loses its connectivity with a PEER-C-MAPPER
inside other domains whether a PIM-NG-DOMAIN or a PIM-NG-CORE-
DOMAIN it MUST NOT immediately remove the multicast sources
received from that PEER-C-MAPPER .instead in such a case the C-
MAPPER MUST set a 5 minute timer by-default which is called the
source-suspension timer and inform other PEER-C-MAPPERs about
the incident by sending AMMT with the sources it has been
receiving from that PEER being entered as suspended. This way
the C-RPs inside other domain will see the suspend flag and will
know that they MUST NOT answer to client requests sent for those
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sources until further notice ,which will be either activating
the sources again or removing them.
16- If a C-MAPPER loses its connectivity with a PEER-C-MAPPER
inside the same domain, it MUST only set the suspend flag for
the sources that the lost PEER was receiving from outside
domains. This is due to the fact that when inside a domain a C-
MAPPER is dead C-RPs will use other existing C-MAPPERs
immediately. So there will be no need to set the suspend flag
for the sources that are being generated inside the domain.
17- C-MAPPERs MUST remove any private DOMAIN or sub-domain number
before advertising any multicast source to peer C-MAPPERs inside
the domain or globally to a peer C-MAPPER in another domain.
18- C-MAPPER or PPER with peers in other domains MUST remove the
additional prepended
The bellow specifications and rules apply to PIM-NG-CORE-DOMAIN (CD):
1- PIM-NG-CORE-DOMAINs number MUST be globally unique to be able
to advertise any multicast source meant to be used globally by
any user connected to the World Wide Web.
2- PIM-NG-CORE-DOMAIN number assignment MUST be done by an
international organization such as IANA.
3- A PIM-NG-CORE-DOMAIN can be simply consisted of one or more C-
MAPPERs and PERs in the core of an enterprise network to
advertise the multicast sources received from peer C-MAPPERs in
connected PIM-NG-DOMAINs of the enterprise. Or can be the
internet backbone of a country connecting the countries network
infrastructure to other countries internet backbone.
4- A PIM-NG-CORE-DOMAIN can be the backbone of an Internet Service
Provider (ISP) from its customer's point of view. in this case
if a customer has 2 different networks connected through an ISP,
if it needs to advertise its multicast sources globally it will
need to do it through the ISP's PIM-NG-CORE-DOMAIN if it doesn't
wish or doesn't need to receive a unique core domain number, by
peering at least one C-MAPPER in one of its domains with a C-
MAPPER inside ISP backbone.
5- A PIM-NG-CORE-DOMAIN can be either a public network or a
private network which is connected to the public network by
using the NETWORK ADDRESS TRANSLATION. And by private PIM-NG
specification means that all the components of the PIM-NG domain
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such as C-MAPPERs and even sources can use private unicast
addresses.
6- If an enterprise does not wish to advertise its multicast
sources globally but needs to use one or more PIM-NG-CORE-
DOMAIN'(s) it can freely use a domain value from the private
range. But in case they need to advertise any multicast source
globally to be used by users connected to other PIM-NG-CORE-
DOMAINs, it MUST apply to get a unique domain number.
7- If an enterprise is using private PIM-NG-CORE-DOMAIN numbers
for its internal use and needs to advertise its multicast
sources globally without getting a unique PIM-NG-CORE-DOMAIN
number, it can do so by applying to get a locally unique PIM-NG-
DOMAIN number to advertise its multicast sources through the
Regional Internet Registry's PIM-NG-CORE-DOMAIN. In this case
the private core domain number must be set to be a sub-domain of
the assigned PIM-NG-DOMAIN number, which the related concepts
will be discussed later.
8- CORE-DOMAIN C-MAPPERs are responsible for connecting different
CORE-DOMAINs to each other.
9- A C-MAPPER MUST add its domain number to the domain-set of any
received multicast sources received from PEER-C-MAPPERs in other
domains before advertising them to other PEER-C-MAPPERs in other
domains.
10- A C-MAPPER inside a PIM-NG-CORE-DOMAIN MUST add its domain
number to the domain-set of any received multicast sources from
other domains when advertising to a PEER-C-MAPPER inside the
same domain. These additional prepended domain values will be
use by C-MAPPERs inside the domain for RPF check.
11- A C-MAPPER inside a PIM-NG-CORE-DOMAIN MUST add its domain
number to the domain-set of any received multicast sources from
peer C-MAPPERs inside the domain to a PEER-C-MAPPER inside the
same domain. These additional prepended domain values will be
use by C-MAPPERs inside the domain for RPF check.
12- C-MAPPERs MUST remove any private DOMAIN or sub-domain number
before advertising any multicast source globally or to be more
specific to a peer C-MAPPER in another CORE-DOMAIN.
13- A C-MAPPER MUST remove additional domains in domain-set of a
received multicast source from a PIM-NG-DOMAIN, except the first
domain number in the domain-set which shows the domain in which
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a source is generated, when advertising a multicast source to a
neighbor PIM-NG-CORE-DOMAIN.
14- A C-MAPPER MUST NOT remove additional domains from the domain-
set of a received multicast source when advertising to PEER-C-
MAPPERs inside a PIM-NG-DOMAIN.
15- If a C-MAPPER loses its connectivity with a PEER-C-MAPPER
either inside the same domain or other domains whether a PIM-NG-
DOMAIN or a PIM-NG-CORE-DOMAIN it MUST NOT immediately remove
the multicast sources received from that PEER-C-MAPPER .instead
in such a case the C-MAPPER MUST set a 5 minute timer by-default
which is called the source-suspension timer and inform other
PEER-C-MAPPERs about the incident by setting the SUSPEND flag
inside the A-MULTICAST-MAPPING-TABLE for the sources it has been
receiving from that PEER and send the table with the suspend
flag to other peers. This way the C-RPs inside other domain will
see the suspend flag and will know that they MUST NOT answer to
client requests sent for those sources until further notice
,which will be either activating the sources again or removing
them.
16- If a C-MAPPER loses its connectivity with a PEER-C-MAPPER
inside the same domain, it MUST only set the suspend flag for
the sources that the lost PEER was receiving from outside
domains. This is due to the fact that when inside a domain a C-
MAPPER is dead C-RPs will use other existing C-MAPPERs
immediately. So there will be no need to set the suspend flag
for the sources that are being generated inside the domain.
17- CORE-DOMAIN C-MAPPER'(s) MUST introduce any existing CORE-
DOMAIN TR'(s) to normal domains for further use.
18- CORE-DOMAINs MUST have one or more TR'(s).
4.6.1.2. PIM-EDGE-ROUTER (PER/PPER)
As described in the previous section each domain is distinguished
from the other domains by a unique domain number.
Each domain MUST be completely isolated from the other domains, and
in case for example all domains are located under one roof inside one
network infrastructure and using one united dynamic routing protocol
it is strongly advised to use PERs to reduce the propagation of
unnecessary multicast introduction message of C-MAPPERs or C-RP'(s)
in search of their peers.
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An example of such network can be an enterprise network trying to
divide its current network infrastructure in to 2 or more PIM-NG
multicast domains or Sub-Domains. If these connected multicast
domains are not isolated somehow we will see unnecessary multicast
traffic inside each domain, which in the PIM-NG case will be the
multicast traffics related to C-MAPPER introduction messages to ALL-
PIM-CLIENTs(239.0.1.190) or C-RP introduction messages(239.0.1.189)
sent out to find PEER-C-RPs which are intended to circulate inside
one domain and since PIM-NG-ROUTERs inside other domains wont react
to such messages from other domains it will be a waste of network
resources.
Another example could be the World Wide Web itself, in which each
multicast domain is connected to other multicast domains by either
using one or more edge routers connected to other multicast domains
by using MP-BGP or a simple tunnel between each 2 multicast domain to
give multicast traffic transfer ability. And such designs are due to
the fact that in reality not all routers between each multicast
domain support the needs of multicast traffic transfer.
Because of the above facts PIM-NG introduces the concept of PIM-EDGE-
ROUTER with 2 different classifications:
1- PIM-EDGE-ROUTER(PER):a PER is simply a PIM-NG-AWARE router that
acts as the boundary between either 2 PIM-NG domains, Sub-Domain
or a domain and outside networks and will control the propagation
of unnecessary or unwanted PIM-NG introduction messages.
2- PRIVATE-PIM-EDGE-ROUTER (PPER): a PPER is a PIM-NG-AWARE router at
the edge of the network which is responsible for NETWORK ADDRESS
TRANSLATION (NAT) operations. PPER is responsible of becoming peer
with other PPERs in other domains in order to exchange AMMT'(s)
between different private PIM-NG domains. It is seen as a normal
C-MAPPER by other domains, and is seen as PPER by internal C-
MAPPERs in a way that an existing C-MAPPER inside the domain will
only exchange the contents of AMMT with a PPER and won't introduce
it to the domain.
Below specifications and rules apply to PIM-EDGE-ROUTERs (PER):
o A PIM-NG-AWARE router connecting 2 or more PIM-NG multicast
domains to each other is considered a PIM-EDGE-ROUTER(PER)
o A PIM-EDGE-ROUTER connecting a public PIM-NG domain to other
PIM-NG multicast domains is called a PER. And by public PIM-NG
specifications means that either every PIM-NG-AWARE router
inside the domain is using public class IPs or at least C-
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MAPPERs or ALL-SOURCES inside the domain use public IP
addresses. In the case of public PIM-NG multicast domain ,if the
domain is connected to other domains by a protocol capable of
transferring multicast traffic ,such as MP-BGP it is advise to
put the PER at the edge of the network. If PERs in separate
domains are connected by using a tunnel, they can be placed
anywhere.
o PERs can use an interface loopback as their unicast address
when introducing to C-MAPPERs or any other interface connected
to the DOMAIN.
o Since all interfaces of a PIM-NG-AWARE ROUTER are considered
internal interfaces by default, a PIM-NG PER MUST have one or
more external interfaces connected to the outside networks or
domain. so a PER can have one or more interface inside domain[X]
and one or more inside domain[Y].
o A PER MUST NOT forward any multicast introduction messages
received on an internal interface to its external interface.
Unless it is dictated to the PER to forward a specific multicast
introduction which MUST BE done based on the domain number
indicated in the introduction message.
o A PER can act as the boundary between to C-MAPPER Mesh-Group
Areas inside a domain to prevent the propagation of ACTIVE C-
MAPPER introductions from one area to the other area. In this
case the PER MUST BE configured to have one or more interface in
each area. These areas are ONLY meaningful to the PER, so that
the PER will not forward multicast introductions from one area
to the other one.
o A PER which is acting as the boundary between Sub-Domains, MUST
know the main domain number in which it is resided and also the
Sub-Domain numbers to which it is connected. This is duo to the
fact that in some designs the need for multicasting in PIM-NG
will need the PER to forward the ACTIVE C-MAPPER introduction
messages sent to 239.0.1.190 in the main domain by checking the
domain number of the received introduction messages. The
concepts related to Sub-Domain are explained in section 4.6.5. .
o A PER acts as the boundary between 2 domains, Sub-Domains and
areas, so it MUST NOT forward multicast introduction messages
sent to 239.0.1.188, 239.0.1.189, 239.0.1.190 received from one
domain, Sub-Domain and area to the other. ONLY in case of Sub-
Domain and Area a PER acting as the boundary between the 2 can
forward such traffic and ONLY if it is dictated to do so.
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o A PER can act as a BORDER-PIM-NG-ROUTER (BPR) when connecting a
PIM-NG domain to a PIM-SM domain. In such designs PER MUST have
one or more hands or interfaces in PIM-NG domain and one or more
hands in PIM-SM domain.
o A PER MUST introduce itself to the closest C-MAPPER only in
case, it has the role of a BPR too, so that the C-MAPPER starts
sending AMMT to the PER. PER will use the contents of AMMT in
the process of forwarding join/prune messages received from the
connected PIM-SM network to the PIM-NG network.
o If in a network design such as a network containing PIM-NG SUB-
DOMAINs ,it is needed that the PER forwards the multicast
traffic destined for 239.0.1.188 and 239.0.1.190 in the main
domain ,it MUST become aware of the situation to be able to
forward that specific traffic.
o In case TR exists in the domain, each PER MUST set the R-BIT of
the Source Unicast Address which shows that the join/prune
message MUST be forwarded towards the TR first and put the
address of the closest TR in the appropriate field before
forwarding it in the domain.
The bellow specifications and rules apply to PRIVATE-PIM-EDGE-
ROUTERS (PPER):
o A PIM-EDGE-ROUTER connecting a private PIM-NG multicast domain
to other domains ,whether private or public ,and typically is
responsible for doing the NETWORK ADDRESS TRANSLATION will
introduce itself as a PRIVATE-PIM-EDGE-ROUTER(PPER) to the C-
MAPPERs inside the domain. It will be done by the EDGE-ROUTER at
the time of introducing itself to the C-MAPPER, and by setting
the PRIVATE (P)-BIT in the introduction message. And by private
PIM-NG specifications means that all components of the domain
such as C-MAPPERs and even sources use private IP addresses, or
at least some of the sources inside the domain are using private
addresses which need to be accessed from the outside.
o In a network design in which all C-MAPPERs inside the domain
are using private unicest addresses, PPER is responsible of
becoming PEER with other PPERs or C-MAPPERs in other domains in
order to provide the ability of exchanging the information
regarding the existing multicast sources in different domains,
through exchanging the AMMT between PPERs or C-MAPPERs in other
domains and C-MAPPERs inside their own domain. So in such a
design a PPER is seen as a PEER-C-MAPPER by PPERs or C-MAPPERs
in other domains and MUST also be configured as a C-MAPPER.
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o A PPER is seen as only a PPER by C-MAPPERs inside the domain
and the information related to it such as the unicast address,
MUST NOT be advertised inside the domain in C-MAPPER
introduction messages sent to 239.0.1.190. Such information is
only usable by existing C-MAPPER'(s). And C-MAPPER uses the
information regarding PPER to send the contents of AMMT to the
PPER'(s).
o In designs in which at least one C-MAPPER inside the domain is
using publicly routable IP address, and is configured to
directly become peer with C-MAPPER'(s) or PPER'(s) in other
domains on behalf of the domain a PPER may not need to play the
role of C-MAPPER too, and will only play the role of PPER and
receive the A-MULTICAST MAPPING TABLE for further use.
o In a network design in which all C-MAPPERs inside the domain
are using private unicast addresses ,PPER is responsible of
becoming MSDP-PEER with RP'(s) inside any neighboring PIM-SM
domain , in case each domain needs to become aware of the
sources that are being generated in the other domain.
o A PPER can act as a BORDER-PIM-NG-ROUTER (BPR) when connecting
a private PIM-NG domain to a PIM-SM domain. In such designs PER
MUST have one or more hands or interfaces in PIM-NG domain and
one or more hands in PIM-SM domain.
o Each PPER MUST send unicast introduction messages to the
unicast address of the closest C-MAPPER, Introducing itself so
that the C-MAPPERs can start sending their A-MULTICAST MAPPING
TABLEs.
o To find the closest C-MAPPER, a PPER MUST listen to the
introduction messages sent by the C-MAPPER in the domain or in
case of existing C-MAPPER Mesh-Groups the introduction messages
sent by the Active C-MAPPER.
o In case of a multicast domain with more than one C-MAPPER Mesh-
Group isolated and separated in to 2 or more Mesh-Group areas by
setting up boundaries using PERs, it is STRONGLY advised to
statically introduce at least one C-MAPPER from other Mesh-
Groups to the PPER. This is a MUST due to the fact that the PPER
will definitely hear the introduction message of the active C-
MAPPER in area it is resided in, but it needs to also be aware
of at least one C-MAPPER from the other Mesh-Groups.
o Each PPER MUST inform the C-MAPPERs inside the domain about the
received multicast sources from other domains by sending the
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AMMT to the closest C-MAPPER to which it has introduced itself
to in the first place.
o When a PPER receives information regarding multicast sources
inside its own domain, since it is at the edge of a private
network it MUST first save the information related to the
unicast address of each source with private IP address in a
table specific to PPER called INTERNAL-MULTICAST-SOURCE TABLE
(IMST) and then it MUST change the unicast address of the
sources with its public unicast address before sending the AMMT
to PEER PPERs or MSDP-PEERs. The process of changing source
unicast address of multicast groups MUST be done based on an
existing ACL or route-map, due to the fact that some multicast
groups may use public unicast addresses, and we don't want
ending up changing those addresses too. So if a source unicast
address needs to be changed it MUST be chosen by an ACL.
o If a PPER receives a join/prune message on an external
interface with its own unicast address as the source of the
multicast group, it MUST check the contents of IMST and find the
real unicast address of the source that is originating traffic
for multicast group (G) and replace it with the address inside
the join/prune message and forward it to the domain.
o If a domain is connected to outside networks through more than
one PPERs , and each PPER is acting as a C-MAPPER to become peer
with PPER'(s) or C-MAPPER'(S) in other domains on behalf of C-
MAPPERs inside its domain , a mechanism MUST BE used so that all
the PPERs use one united publicly routable IP address as the
originator address of the sources that are originated inside the
domain, and also in case there are multicast sources using
private IP addresses that must be advertised to other domains,
as the source unicast address of such multicast sources. This is
due to the fact that we don't want to end up advertising our
multicast sources with different originator address or source
unicast addresses to other domains. So we advise that on each
PPER a united publically routable address be configured as the
originator address if the PPERs also have the role of C-MAPPER.
o In case TR exists in the domain, each PPER MUST set the R-BIT
of the Source Unicast Address which shows that the join/prune
message MUST be forwarded towards the TR first and put the
address of the closest TR in the appropriate field before
forwarding it in the domain.
o EACH PPER MUST change the originator unicast address of the
sources created inside its domain with its own public address.
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This address or the originator unicast address will be used in
case a PIM-SM domain is needed to become connected to a network
of PIM-NG domains in the process of RPF check.
o PPER MUST maintain connectivity with C-MAPPER through its
unicast introduction messages and in case it loses its
connectivity with the C-MAPPER and if SC-MAPPER exists, it MUST
immediately query the SC-MAPPER. This is duo the fact that a
PPER is acting as the C-MAPPER and any existing SC-MAPPER from
the peer C-MAPPER's point of view. PPER MUST send periodic
introductions every 30 seconds.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P|Z|B| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EDGE unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| A-MULTICAST MAPPING TABLE |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 39 PER introduction message
o TYPE :EDGE
o Z-BIT: whenever a PPER needs to inform a change about its
connected neighbor DOMAINs to C-MAPPER it will set this BIT
and then send the information.
o P-BIT: when set indicates to the receiving C-MAPPER that it
is a PPER.
o B-BIT: Border-PIM-NG-ROUTER BIT is set when a PER has the
role of BPR.
+---------------------------------------------------+
|source address | Destination Group| source host |
+---------------------------------------------------+
| | | |
+---------------------------------------------------+
| | | |
+---------------------------------------------------+
Figure 40 Internal Multicast Source Table
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4.6.1.3. Tree Root (TR)
Up to this point of explaining PIM-NG specifications, although the
existence of a component named TR was mentioned, clients were to make
direct contact with a source and send their join message directly to
the desired source. The processes have been explained this way to
give a good understanding of the underlying processes.
They still can, but to support the needs of multicasting, PIM-NG
introduces the concept of TREE-ROOT (TR). This concept has been
introduced, duo to the fact that, there might be many clients in each
domain in need of listening to a particular multicast traffic and if
they were all to send their join messages directly to that source or
the TR residing in the core domain, the final result will be the
waste of bandwidth and the waste of source and CORE-DOMAIN-TR
resources.
The below specifications apply to TR:
o Each normal domain can have one or more TR'(s) which it is
strongly advised to be used.
o Each core-domain MUST have one or more TR'(s).
o ALL-PIM-NG-TR'(s) MUST introduce themselves to the closest C-
MAPPER by sending uicast introduction messages ,so that the C-
MAPPER learns the TR's unicast address and introduce it to the
domain .
o If any core-domain is considered, the C-MAPPERs inside the
core-domain MUST introduce any existing TR inside the core-
domain to all normal domains connected to it so that the entire
PIM-NG multicast network will become aware of the existence of
core-domain TR'(s).
o If a TR is receiving multicast traffic (G), and other TR'(s)
exist in the domain, it MUST make the other TR'(s) aware of the
traffic it is receiving by sending an introduction message
containing the JOINED-GROUP-TABLE, to the unicast address of the
other TR'(s) it receives from C-MAPPER inside PDTT. This is done
due to fact that other clients may become interested in
receiving such traffic later, so if they send their join to
another TR which is closer to them and not aware of the
multicast traffic, it can be double act of sending joins out of
a domain and a waste of resources.
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o When a TR receives a join/prune message with the R-BIT of
Source Unicast address being set, which means that the message
MUST reach the desired TR first, it MUST check the address of
the TR and if the address is its own address it MUST clear the
R-BIT, which means that the message has reached the desired TR
in the domain and then forward it towards the desired source.
o If in a PIM-NG multicast domain more than one TR exists, and a
TR receives a join/prune message for (S, G), before clearing the
R-BIT and forwarding the message to the next hop, it MUST first
check its JOINED-GROUPS TABLE to see if other TR'(s) has joined
the SPT for that (S, G). and if an entry is found in the JOINED-
GROUP table received from other TR'(s), then if and ONLY IF the
cost of reaching the TR which already joined the SPT for (S,
G)based on the calculations done by the underlying unicast
routing protocol is better than the cost to reach the source, it
MUST leave the R-BIT and MUST NOT clear it and MUST put the
address of the TR which has already joined the SPT for (S,G) in
the appropriate field and forward the join/prune message to the
next hop in the best path towards that TR. Otherwise in case the
cost of reaching the source is better than the cost of reaching
the next TR which is already joined the SPT for (s, G), it MUST
clear the R-BIT and forward the join/prune message to the next
hop in the best path towards the source.
o If an RP has the role of TR, receiving a join/prune message of
(*, G, RPT) with the RP address as the TR address means that the
RP MUST NOT send back the (S) for (G) to the client and MUST
find that source unicast address of (G) in either MMT or AMMT
and put the address in the appropriate field and forward the
packet towards the source.
o If a TR is also a C-RP, then TR introduction messages MUST NOT
BE sent and only a C-RP introduction message with the TR-BIT set
WILL be enough.
o Each TR MUST maintain connectivity with the C-MAPPER by sending
periodic introductions every 30 seconds.
At the end it must be noted that the TR do not need to be a separate
component, and each existing C-MAPPER or C-RP in the domain is the
best choice to also play the role of an TR. But PIM-NG specifications
STRONGLY advise the use of C-RP if it is a must.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| D O M A I N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Z| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TR unicast address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| JOINED GROUP TABLE |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 41 TR introduction message
oType : TR
o Z-BIT: if set indicates to the receiver that there has been a
change in the joined-group-table.
+------------------------+
| JOINED-GROUP1 |
+------------------------+
|MULTICAST GROUP (G) |
+------------------------+
|SOURCE UNICAST ADDRESS |
+------------------------+
| . |
+------------------------+
| JOINED-GROUP N |
+------------------------+
|MULTICAST GROUP (G) |
+------------------------+
|SOURCE UNICAST ADDRESS |
+------------------------+
Figure 42 Joined-Groups table used by both TR'(s) and Clients
4.6.1.4. Domain-set and RPF check
PIM-NG Domain-Set is similar to BGP AS-Path sequence in a way that
each C-MAPPER MUST add its PIM-NG domain number to the domain-set of
any multicast source before advertising it to a peer C-MAPPER .so at
the end Domain-Set of a multicast source is a string of domains a
multicast source has passed to reach its current domain or better to
say to reach the C-MAPPER inside the current domain. From this
perspective Domain-Set can be called Domain-Path sequence.
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Domain-set is what a PIM-NG C-MAPPER uses to RPF check a multicast
source it receives from its peer in other domains. Unlike the RPF
check method used in PIM-SM and MSDP which has some limitations like:
o The network of multicast domains cannot have a transitory AS,
due to the fact that for a Source Active message to pass the
RPF check, the first AS in best path to the originator RP MUST
BE equal to the MSDP peer. So if a customer's Autonomous
System is connected to an ISP's Autonomous system, the RP
inside the customer network must be MSDP peer with the RP
inside the ISP network.
o Filtering SA messages can be a hard task, because of the RPF
check rule in a way that, you cannot have a transitory AS
between to autonomous systems. such a case can be seen when
administrators does not wish to update all of the SAs or some
of the SAs created inside their PIM-SM domain to the neighbor
Autonomous System , but they need to update them to a MSDP-
PEER in an Autonomous System which is (i.e.)2 AS away.
o . . .
The RPF check method used in PIM-NG provides the ability of having
transitory Autonomous Systems. Examples of such designs are:
o Different PIM-NG domains are connected by an ISP's backbone and
the ISP is only needed to provide UNICAST-REACHABILITY between
different PIM-NG domains or different Autonomous Systems.
o an enterprise does not wish to update all of its multicast
sources to the neighbor Autonomous System or PIM-NG multicast
domain , but it needs all of its multicast sources to be
advertised to an AS which can be reached through this AS.
consider the bellow illustration in which (i.e.) AS1 needs to
advertise its multicast sources to AS3 and AS4 but doesn't
want AS2 to become aware of those multicast sources or at
least part of the multicast sources :
AS1 (D1) ----AS2 (D2) ----AS3 (D3) ----AS4 (D4)
MSDP specifications suggest that such work cannot be done and
there will be a RPF check failure. But in PIM-NG such a work
can be done.
So if a source (S) is generating multicast traffic (G) in AS1 which
is assigned a PIM-NG domain number of 1(D1) in the above
illustration, the C-MAPPER inside D1 will advertise the (S,G) with
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the domain-set (1) to the peer C-MAPPER in D2 and likewise the C-
MAPPER in D2 will advertise the (S,G) to its peer in D3 with domain-
set of (1,2) and at the end the C-MAPPER inside D4 will receive the
(S,G) with domain-set (1,2,3).
The bellow rules apply to the DOMAIN-SET:
o Each C-MAPPER or PPER MUST add its domain number to the domain-
set of a multicast source before advertising it to its peers in
other domains.
o If inside a domain , more than one C-MAPPER is considered, each
C-MAPPER MUST add its domain number to the domain-set of a
multicast source before advertising it to its peers inside the
domain, unless the C-MAPPER MESH-GROUP concept is in use. This
process is more like prepending the domain number to the domain-
set.
o If A C-MAPPER(i.e. C-MAPPER-A) is a member of more than one
Mesh-Group, or a member of a Mesh-Group and also is peer with a
C-MAPPER which is a member of another Mesh-Group, which in this
case C-MAPPER-A is acting as a connection or bridge between the
2 Mesh-Groups, and it receives an update regarding a multicast
source from a peer inside the same Mesh-Group, it MUST prepend
its Domain number to the Domain-Set of the multicast source
before advertising it to its peers in other Mesh-Groups.
o A C-MAPPER or PPER MUST remove any prepended domain numbers
from the domain-set of a source received from C-MAPPERs inside
the domain , before advertising the multicast source to a peer
C-MAPPER or PPER in other domains.
o Since the PIM-NG-DOMAIN numbers are only significant from a
connected PIM-NG-CORE-DOMAIN point of view, C-MAPPERs or PPERs
in a CORE-DOMAIN MUST remove any PIM-NG-DOMAIN number, EXCEPT
the domain number associated to the domain in which a multicast
source resides, from the domain-set of a multicast source before
advertising it to C-MAPPERs or PPERs in other PIM-NG-CORE-
DOMAINs.
o C-MAPPERs or PPERs in a CORE-DOMAIN MUST NOT remove any PIM-NG-
DOMAIN number from the domain-set of a multicast source before
advertising it C-MAPPERs or PPERs in other PIM-NG-DOMAINs which
are connected to it and need to receive the updates regarding
those multicast sources.
PIM-NG RPF check method uses the bellow rules:
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o The (S, G) update received in the AMMT with the shorter domain
sequence in Domain-Set passes the RPF check.
(S,G,D1)
(S,G)AS1(D1)---------AS2(D2)-----------AS4(D4)
| /
| /
(S,G,D1)| /(S,G,D1,D3)
| /
| /
AS3(D3)
Figure 43 Inter-domain connectivity and RPF check
As shown in Figure 43 a multicast source (s) in AS1 with PIM-NG
domain number 1(D1) is generating multicast traffic destined to
(G) and the C-MAPPER in the domain is advertising the (S, G) to
its peers in D2 and D3. C-MAPPERs in D2 and D3 receive the
update. C-MAPPER in D3 advertises the (S, G) to its peer in D2
with the domain-set (D1, D3). C-MAPPER in D2 receives 2 updates
for (S,G) with different domain-sets , one is (D1) and the
other is (D1,D3) . So at this point the update received from D1
passes the RPF check and the update received from R3 fails the
RPF check.
o If there is a tie in the domain-set of a multicast source
received from peers in 2 different domains , the update
received from the sender in the best path towards the
originator according to the unicast routing information MUST
pass the RPF check. In the above example if D3 is connected to
D4 by making a C-MAPPER from each domain peer with the other
one, then C-MAPPER in D4 will receive the update about (S, G)
with equal domain sets of (D1, D2) and (D1, D3), which in this
case the update received from the C-MAPPER in D2 which is in
the best path towards the originator C-MAPPER in D1 passes the
RPF check.
o If inside a domain more than one C-MAPPER exists and the MESH-
GROUP concept is not used, the above rules MUST be followed.
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(S,G,D1)
(S,G)C-MAPPER1-D1--------------C-MAPPER2-D1
\ /
\ /
(S,G,D1)\ /(S,G,D1,D1)
\ /
\ /
C-MAPPER3-D1
Figure 44 Intra-Domain connectivity and RPF check
As illustrated in Figure 44,in which C-MAPPER1 is advertising
an update about a newly originated source (S,G) with domain-set
(D1) to its peers C-MAPPER2 and C-MAPPER3.C-MAPPERs 2 and 3
receive the update and start advertising the update to each
other , so at this point and after the advertisement C-
MAPPER2(i.e.) receives another update for (S,G) from C-MAPPER3
with domain-set (D1,D1) and since the domain sequence of the
second received update from C-MAPPER3 is longer than the one
received from C-MAPPER1 , it fails the RPF check.
o The above rules are applicable in different situations
regarding RPF check, and bring so much flexibility to work with
multicast sources and the updates regarding those sources.
o If a C-MAPPER inside a CORE-DOMAIN receives an update about a
multicast source from a peer C-MAPPER in a CORE-DOMAIN and ALSO
from a peer C-MAPPER in a PIM-NG-DOMAIN , the update received
from the peer in CORE-DOMAIN MUST pass the RPF check without
considering the DOMAIN-SET.
4.6.2. Inter-domain connectivity concepts
PIM-NG Inter-domain connectivity is mainly focused on the processes
involved in exchanging the information regarding multicast sources
being originated in different multicast domains, as for now like PIM-
SM, PIM-NG uses the underlying unicast routing protocol information
in order to send join/prune messages from a client in need of
receiving a multicast traffic to the final destination which can be a
server generating the multicast traffic.
Although, PIM-NG specification processes and features are designed in
a way that makes it possible to use a multicast routing protocol
unique to PIM-NG in order to send join/prune messages from a receiver
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client to the originator of a multicast traffic, but since it is out
of the scope of this document ,we are going to only explain the
processes related to connecting 2 multicast domains and exchange the
A-MULTICAST MAPPING TABLE'(s) between them ,which shall be enough to
find a source and through using the underlying unicast routing
protocols information reach the source.
The related concepts are going to be explained in 2 different
sections, which are Public Domain connectivity and Private Domain
Connectivity.
4.6.2.1. Public Domains
A public domain is considered by PIM-NG specifications to be either a
domain in which C-MAPPERs and sources use public IP addresses or a
domain divided in to 2 domains or sub-domains in which the unicast
address of C-MAPPERs and existing multicast sources are known to the
population, and there is no need to use a PPER and domains are
separated by PER'(s) which act as the domain boundary.
Concepts are explained in 2 different sections called inter-domain
concepts and intra-domain concepts. Inter-domain section is focused
of connectivity of 2 different PIM-NG domains in terms of exchanging
information regarding originated multicast sources in each domain and
the process in which a CLIENT sends join/prune message to a source.
And intra-domain section which is the following section is focused
mainly on the communication between any existing TR with C-MAPPER and
finally clients, which is actually the only feature of PIM-NG
specifications that hasn't been described yet.
4.6.2.1.1. Intra-domain concepts
As said before, TR is responsible of sending join messages on behalf
of CLIENTs inside the domain to a source inside the domain or other
domains.
If CORE-DOMAIN implementations are considered and CORE-DOMAINs do
exist, and the domain-set of a multicast source indicates that the
source of the multicast traffic can be reached by passing a PIM-NG-
CORE-DOMAIN then the client creating the join/prune message MUST set
the C-BIT of source unicast address and put the address of the CORE-
DOMAIN-TR in the appropriate field and then send the message to the
next hop.
But first a PIM-NG-AWARE-ROUTER inside each domain must be chosen to
act as the TR. and as mentioned before; each existing C-MAPPER can
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take the role of a TR to, which eliminates the need for a separate
router to be used.
Commands such as the commands bellow are initiated on the chosen
router:
The above command lines will tell the router that it is the TR of
PIM-NG domain X ,and it should use its interface loopback defined in
the command as the unicast address it is going to introduce itself
with it to the C-MAPPER.
Although it may seem useful to have backup TR in the domain, we
advise the use of a new TR instead of backup TR for bringing both
redundancy and high availability at the same time to the domain. So
no back-up TR is considered .the only case which there might be a
back up TR implementation is when a C-RP has the role of TR and a SC-
RP is considered.
In case C-RP'(s) is going to have the role of TR too, and the concept
of ANYCAST-RP is in use in the domain, the following rules MUST be
obeyed:
o Since ANYCAST-RP concept causes the clients to contact the
closest RP unicast address according to their unicast routing
tables, if C-RP is going to act as a TR, then ALL-C-RPs in a
multicast domain MUST be configured to act as a TR too.
o The active C-MAPPER MUST become aware of the situation which
can be done by a command line initiated on ALL-C-MAPPERs. So the
active C-MAPPER introduces only one TR unicast address which
will be the ANYCAST address used for C-RPs.
o Each TR in this particular design MUST use 2 different
addresses. One for the ANYCAST address and one for introducing
itself to the closest C-MAPPER. The addresses MUST be the
addresses used for C-RP processes which had been explained
before.
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o C-MAPPERs then MUST introduce ALL the other TRs to each TR they
find, inside the PDTT sent with the unicast-encapsulated
introduction messages they send to each TR. This MUST be done so
that TRs can send their JOIN-GROUP TABLE to each other.
After the TR is configured it will do the following processes:
1- It waits to hear the introduction message of the C-MAPPER sent to
239.0.1.190 to learn its unicast address.
2- As soon as TR receives the C-MAPPER introduction it will update
its internal PDTT with the address of C-MAPPER and other
information included in the table.
3- TR starts to send unicast introduction messages to the unicast
address of C-MAPPER, which includes its unicast address.
4- TR will send these introductions as keep-alive messages every
30sec to the C-MAPPER.
5- If it's joined to any multicast group (G), and by joining we mean
receiving traffic for that group, it MUST put an entry for that
group in its JOINED-GROUP-TABLE for further use.
6- If in the introduction received from the C-MAPPER it receives
the address of other TRs, it MUST send its JOINED-GROUP-TABLE to
other TRs by sending unicast TR introduction messages to the
address of those TRs. This MUST be done so that if a new client in
another side of the domain sends a join for the same group to
another TR, the TR will only send a join for that group to the TR
which is already receiving the traffic for the group (G).
7- The introduction messages between different existing TRs are only
sent at the time, there is a change in the JOINED-GROUP-TABLE by
setting the Z-BIT. This is due to the fact that TR'(s) communicate
with C-MAPPER and this communication and periodical introductions
acts as a keep-alive so there will be no need for the TRs to send
periodical introductions as Keep-Alive to each other.
After the C-MAPPER receives an introduction from the TR it will:
1- Update its PIM domain topology table, and send an introduction
message to ALL-PIM-NG-CLIENTS for further use.
2- C-MAPPER maintains connectivity with the TR by sending unicast
acknowledgement every 30 second back to the TR in response to TR
introduction.
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3- If ANYCAST concept is needed to be implemented in a domain with
more than one TR , then the C-MAPPER MUST know the address used as
the ANYCAST address and only send that address to ALL-PIM-NG-
CLIENTs.
4.6.2.1.2. Inter-domain concepts
In a Public PIM-NG Multicast domain a C-MAPPER can directly become
peer with a C-MAPPER in another domain. And ALL Multicast Sources use
public IP addresses. The processes regarding to peering the C-MAPPERs
are much like the processes related to peering C-MAPPERs inside the
same domain. The only difference between the concepts is:
o A C-MAPPER MUST NOT send a multicast C-MAPPER introduction
message to find its peer in another domain. Instead a C-
MAPPER'(s) MUST send a unicast-encapsulated C-MAPPER
introduction message to the unicast address of its peer in
another domain.
Figure 45 which illustrates a multicast network with 2 public PIM-NG
multicast domains will be used for further explainations.
Figure 45 network with 2 multicast domains
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For the sake of simplicity in explaining the processes lets accept
the fact that , there is unicast reachability between the 2 domains
by using either a dynamic routing protocol capable of carrying
multicast traffic like MBGP or a tunnel between the 2 domains.
The processes to connect the 2 multicast domains are as follows:
o In Each domain a C-MAPPER which uses a publically routable
unicast address MUST be chosen, so makes it possible to directly
make the C-MAPPERs peers.
o C-MAPPER-WEST (WEST from now one) becomes peer with C-MAPPER-
EAST (EAST from now one) using the unicast address of EAST to
send the introduction message. the same is done on east:
And on east:
o WEST starts sending unicast-encapsulated introduction messages
to EAST every 30 seconds until it receives the unicast-
encapsulated introduction message of EAST.
o After receiving the first introduction message, both C-
MAPPER'(s) MUST send their introduction messages periodically
every 60 seconds to maintain connectivity with each other as
keep-alive messages.
o If any SC-MAPPER is considered in a domain, its address MUST be
introduced to the peer in the introduction message.
o If WEST needs to inform its peer which is EAST about a change
in the contents of AMMT, it MUST set the ZTCN-BIT in the
introduction message and send the AMMT.
o WEST MUST add its domain number to the domain-set of any newly
originated multicast sources before sending an update about it
to EAST. The same MUST be done by EAST.
o Each C-MAPPER will then send the received update from the peer
to the C-RPs residing in the domain
Now bellow the processes related to communication between clients and
sources are explained:
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o A host (H1) in domain1 (D1) wants to receive the multicast
traffic destined for 228.9.9.9(i.e.) which is being generated in
domain2 (D2).
o H1 shows its desire to receive the traffic through IGMP
messages it sends to the upstream router.
o Client 2 becomes aware that a host inside the network behind it
needs to receive the traffic destined for 228.9.9.9.
o Client2 checks its PDTT to find the closest C-RP, and chooses
C-RP-EAST(i.e.).since the RP and existing TR are not the same ,
H1 MUST send a unicast-encapsulated request for source message
to C-RP.
o Client2 sends a unicast-encapsulated PIM-NG request message to
the C-RP. And receives a unicast acknowledge from the C-RP
containing the unicast address of the source generating the
multicast traffic in the format of (10.2.2.10, 228.9.9.9).
o Client2 creates a join/prune message for (10.2.2.10,228.9.9.9)
and since a TR exists in the domain and the domain-set of the
source received from the C-RP doesn't contain any CORE-DOMAIN in
the path , H1 sets the R-BIT of source unicast address and puts
the address of the TR(10.1.1.20) in the appropriate field which
shows that the join/prune message MUST first be sent towards the
TR and sends the join/prune message towards the next hop or PIM-
NG neighbor and joins the (S,G,RPT) rooted at TR which is
considered to be the best path to reach the source.
o TR receives the join/prune message and clears the R-BIT and its
unicast address from the TR unicast address field, and forwards
the message towards the next hop in the best path towards the
source.
o PER-EAST in domain2 (D2) receives a join/prune message on its
external interface for multicast group 228.9.9.9 and must
forward it to the next hop in the best path towards the source
which is 10.2.2.10.
o Since a TR exists in the domain PER-EAST MUST set the R-BIT
again and put the address of TR(10.2.2.20) in the appropriate
field and forward the join/prune message towards the source and
actually join the (S,G,RPT) rooted at TR.
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o The join/prune message reaches the TR in D2, and TR again
clears both the R-BIT and the TR unicast address field and
forwards the message to the next hope.
o Finally join/prune message for multicast destination 228.9.9.9
arrives at 10.2.2.10 and source becomes aware that a client
somewhere is in need of receiving the traffic and it MUST join
the Shortest path tree which is actually the current (S,G,RPT)
rooted at the TRs in each domain. So at the end 10.2.2.10 starts
forwarding the traffic.
Now a new host in D1 which is going to be H2 needs to receive the
same traffic:
o H2 shows its interest through IGMP to the upstream router which
is client3.
o Client3 goes through the same process as client2 to find the
source unicast address of (G) and receives it from closest C-
RP.
o Client3 sends the join/prune message towards the TR.
o TR receives a join/prune message for (S,G) which it already
joined the shortest path tree for it , so without forwarding
the join/prune message any further ,TR starts to forward the
traffic for (10.2.2.10,228.9.9.9) down the new SPT towards
client3.
4.6.2.2. Private domains
A private domain is considered by PIM-NG specifications to be a
multicast domain in which all multicast sources or at least some of
the multicast sources use private IP addresses.
In such a domain:
o If the C-MAPPERs inside the domain use private IP addresses,
then one or more PPER'(s) MUST act as the C-MAPPER to become
peer with C-MAPPERs in other domains on behalf of the C-
MAPPERs inside the domain. And also a mechanism MUST be used
so that PPER'(s) use a united public IP address as the
originator of the multicast sources originated inside the
domain and also as the source unicast address of the sources
using private IP addresses.
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o If C-MAPPER'(s) inside the domain use public IP addresses, then
there is no need for PPER'(s) to have the role of C-MAPPER
too. Although, there might be some multicast designs in which
it is needed for the PPER'(s) to act as C-MAPPER too. In such
domains with a C-MAPPER using public IP address, a mechanism
MUST be used so that the PPER'(s) become aware of the unicast
address that is used by C-MAPPER'(s) as the source unicast
address of the multicast sources using private IP addresses.
In Figure 46 an example network, including 2 private PIM-NG multicast
domains is illustrated. In this example that is going to be used to
explain the processes involved, Domain1 (D1 for simplicity) is a PIM-
NG domain in which ALL multicast sources and the C-MAPPER use private
IP addresses and Domain2 (D2 for simplicity) is a PIM-NG domain in
which the C-MAPPER uses public IP address and is responsible to
directly become peer with a C-MAPPER in D1 and a group of multicast
sources use Public IP Addresses and a group use Private IP Addresses.
In D1 PPER-WEST with the unicast address 192.168.1.10 is going to act
as the C-MAPPER and will become peer with C-MAPPER-EAST (EAST for
simplicity) with the unicast address 192.168.2.10. And in D2 EAST
will become peer with PPER-WEST.
Figure 46 Multicast network with private PIM-NG domains
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Different processes regarding the advertisement of multicast sources
being generated in each domain to the other domain, and how the
join/prune message is going to reach its final destination, are going
to be explained in the following sections.
4.6.2.2.1. Intra-Domain processes
Since most of the processes and concepts regarding the connection
between C-MAPPERs, clients, C-RP and TR in a PIM-NG domain have been
explained up to this point ,processes referred to as Intra-domain
processes will be related to the unexplained parts which are
processes a C-MAPPER and the PPER'(s) are involved in within the
Domain which in our example are D1 and D2 .Before starting to explain
the processes a C-MAPPER and a PER or PPER are involved in ,we are
going to take a look at an example of the steps related to make the
PER ready and after that an example of how to make a PPER ready :
Bellow the processes related to preparing a PER is explained:
o A PIM-NG-AWARE router is chosen to act as the PER.
o a set of commands are initiated on the router:
Or in case the PER is connected directly to 2 domains
Or incase a PER is acting as a BPR:
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o The above set of commands tells the router that it is a PER
inside domain-X .and it MUST bring the interfaces mentioned in
the command set in to the game of PIM-NG.
o Interfaces marked as internal are going to be the ones
connected to the internal domain and the one marked with
external are going to be the ones connected to the outside
networks.
o In case PER is placed right between 2 domains or sub-domains it
MUST have one or more interface inside one domain and one or
more interfaces inside the other domain.
o If a PER is placed between a PIM-NG domain and PIM-SM domain,
It MUST have one or more interfaces inside PIM-NG domain and one
or more interfaces in the PIM-SM domain. Such design may be seen
in enterprise networks migrating from PIM-SM t PIM-NG over a
period of time or in network designs where a PIM-SM domain is
going to be connected to a network of PIM-NG domains or 2 or
more PIM-NG domains are suppose to be connected through either
an ISP's backbone which is still using PIM-SM or a transitory AS
using PIM-SM and the PIM-SM domain'(s)are to be used to forward
the join/prune messages. Such a PER is called a BPR, and the PER
MUST introduce itself to the closest C-MAPPER with the B-BIT in
the introduction message being set. BPR concepts will be
discussed in the appropriate section.
Bellow the processes related to preparing a PPER are explained:
o A PIM-NG-AWARE router at the edge of the domain is chosen to
play the role of PPER. PPER-WEST and PPER-EAST in Figure 46.
o The router MUST be configured and become aware of its role
inside the domain and in case it is going to act as the C-
MAPPER to become peer with other PPERs or C-MAPPERs in other
domains. As before we are going to go through the steps by
initiating some commands on the router to make the process of
explanation easier:
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The above commands tells the router that it is PPER in a PIM-
NG domain[X](D1/D2) .also the above commands dictates to the
router that it has some internal interfaces which are
connected to the inside network and some external interfaces
which are connected to the outside world .
One other thing that the router must become aware of is the
address it must use when introducing itself as the PPER to the
C-MAPPERs inside the domain which in our example is going to
be 10.1.1.50 for PPER-WEST and 10.2.2.50 for PPER-EAST. This
address MUST be an address known to the domain in which the
PPER resides. And it is advised to use a loopback interface as
the source.
o If the PPER is supposed to act as a C-MAPPER too (PPER-WEST in
Figure 46), it MUST become aware of the new role and also MUST
know the address of its peers. one other thing that MUST be
configured is the address that must be used as the C-MAPPER
address which MUST be a public IP address :
Or if the peer PPER is a connected PIM-NG-AWARE router
o The address that is going to be used in the process of finding
and communicating with a peer PPER or C-MAPPER, will be used as
the Originator Unicast Address and source unicast address of the
multicast sources that are originated inside the domain the PPER
resides and use a private IP address. In Figure 44 the address
used for PPER-WEST is 192.168.1.10 in D1 and the address used
for the C-MAPPER-EAST in D2 is 192.168.2.10.
o If the domain is connected to other domains by more than one
PPER a mechanism MUST be used so that if PPERs has the role of
C-MAPPER they all use one united public IP address as the
Originator and source unicast address of the sources that are
originated inside the domain and use private addresses. This is
due to the fact that we don't want to end up advertising our
sources with different source unicast addresses or originator
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addresses ,so PIM-NG specification suggests to configure on all
PPERs an IP address from the public IP address range that is
assigned to the AS or network. This can be done by a command
like:
o if a C-MAPPER inside the domain with public IP address is used
to become peer with C-MAPPERs or PPERs in other domains and the
PPERs doesn't have the role of C-MAPPER they MUST become aware
of the IP address that the C-MAPPER is using as the originator
and source unicast address of the multicast sources that are
generated inside the domain and use private IP addresses. This
MUST be done due to the fact that a PPER may receive a
join/prune message for a multicast source inside the domain
which its unicast address is the address of the C-MAPPER and
will be routed towards the C-MAPPER and that MUST NOT be done.
So we suggest dictating to PPERs that if they receive a
join/prune message on an external interface with the address of
the C-MAPPER as the source unicast address, it IS NOT meant to
be forwarded towards the C-MAPPER and the address MUST be
changed with the real address of the multicast source. this can
be done by a command like the one mentioned above or:
In Figure 46 this address is going to be 192.168.2.10 which is
the address of C-MAPPER-EAST and MUST be set on PPER-EAST.
Processes related to PER will be discussed later when a PIM-NG domain
needs to be connected to a PIM-SM domain. So in this section only
PPER related processes are going to be explained.
o As soon as PPER is configured and becomes aware of its role in
the domain, it MUST communicate with the closest C-MAPPER
according to the information received in the C-MAPPER
introduction message and incase there are more than one C-MAPPER
in domain based on the information it finds inside the PDTT, by
sending an EDGE introduction message. PPER MUST set the P-BIT in
EDGE introduction message which indicates to the C-MAPPER that
it is sent from a PPER. PPER MUST send its unicast address
inside the message so that C-MAPPER'(s) can use it to
communicate with the PPER. So both PPERs in figure 44 start
introducing themselves to the C-MAPPERs inside the domain.
o Each PPER MUST send the introduction messages every 30 seconds
to the C-MAPPER which acts as the keep-alive message.
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o Both C-MAPPERs in D1 and D2 MUST start sending A-MMT'(s) to the
PPERs of their domain. The received information will be used by
PPERs differently, due to the fact that PPER-WEST is also a C-
MAPPER and PPER-EAST is only PPER.
o Both PPERs MUST save the information regarding multicast
sources that are originated inside their domain in IMST for
further use.
o PPER-WEST which has the role of a C-MAPPER too MUST send any
received information regarding the multicast sources being
generated in D1 which it receives from C-MAPPER-WEST to C-
MAPPER-EAST by setting the Z-BIT in the introduction message and
sending the updates inside the A-MMT. If only some of multicast
sources MUST be advertised, it can be done through filtering
process.
o Since ALL multicast sources inside D1 are using private IP
addresses, those multicast sources that are needed to be
advertised to D2 MUST be chosen through an ACL, so that at the
time of updating to C-MAPPER-EAST, PPER-WEST changes the
originator address and source unicast address of those sources
with its own public unicast address which is 192.168.1.10 in
Figure 46.
This can be done by choosing the multicast source addresses
needed to be advertised in an ACL and initiating a command line
(i.e.) on PPER-WEST:
Which dictates to the PPER that it MUST change the originator
address and source unicast address of multicast sources chosen
by the ACL X(i.e.) with its own public IP address or incase
there are more than one PPER with the address indicated by the
command.
o Since C-MAPPER-WEST is not peer with any C-MAPPER in other
domains it MUST maintain connectivity with PPER'(s) of its
domain in order to receive information regarding multicast
sources in other domains and advertise multicast sources in its
domain to other domains.
o In D2, C-MAPPER-EAST is directly involved in the process of
becoming peer with a C-MAPPER in another domain which is PPER-
EAST, so it MUST only send the information regarding multicast
sources being originated inside its domain to PPER-EAST, UNLESS
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it becomes aware that PPER-EAST is also BPR and connected to a
PIM-SM domain, which in this case it MUST send the full A-
MULTICAST MAPPING TABLE which may include multicast sources
being originated in other domains.
o Since C-MAPPER-EAST is going to advertise multicast sources
originated inside the domain (D2) to its peer in D1, it MUST
change the source unicast address of multicast sources
originated inside D2 with private IP addresses, with its own
public IP address which is 192.168.2.10 in Figure 44. It MUST be
done based on an ACL or route-map like what had been done on
PPER-WEST , since there are multicast sources in D2 with public
source unicast address that their address must not be changed.
o Since PPER-EAST is only acting as PPER it MUST become aware
about the address the C-MAPPER is using as source unicast
address when advertising multicast sources with private IP
addresses to other domains, so that when it receives a
join/prune message on its external interface with that source
unicast address, it can act properly. This can be done by
initiating a command line(i.e.) on PPER-EAST like:
Instead of A.B.C.D, the public IP address being used by C-MAPPER
in such process MUST BE used, which in our example is
192.168.2.10.
4.6.2.2.2. Inter-domain concepts
Inter-domain connectivity concepts are mostly focused on the process
of exchanging information regarding multicast sources between the 2
domains and the process through which a CLIENT will send join/prune
message for a multicast group inside another domain which is using a
private IP address inside the destination domain.
First the processes regarding the exchange of A-MULTICAST MAPPING
TABLES between the 2 domains of Figure 46 will be explained and then
to explain the process of sending the join/prune message and
receiving multicast traffic, an example in which hosts in D1 are in
need to receive multicast traffic which is generated in D2 will be
explained.
1- Exchanging AMMT between the 2 domains :
o Since PPER-WEST has the role of C-MAPPER, it will become peer
with C-MAPPER-EAST on behalf of the C-MAPPER-WEST. And C-
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MAPPER-EAST will become peer with PPER-WEST which is seen by
C-MAPPER-EAST as C-MAPPER-WEST or the C-MAPPER residing in
D1.
o Both PPER-WEST and C-MAPPER-EAST MUST use the public unicast
address of the other one to send unicast-encapsulated
introduction messages to both introduce themselves to each
other and exchange the contents of their A-MULTICAST MAPPING
TABLEs which holds the information regarding multicast
sources being originated in either of the domains. So PPER-
WEST MUST use the unicast address 192.168.2.10 (Figure 46)
which is the address of C-MAPPER-EAST, as its peer address.
And C-MAPPER-EAST MUST use unicast address 192.168.1.10
(Figure 46) as its peer address.
o As explained before both PPER-WEST and C-MAPPER-EAST MUST do
some modifications on the information regarding multicast
sources generated inside their domains with private IP
addresses before advertising them to the other domain. So
considering Figure 46 , C-MAPPER-EAST MUST change the source
unicast address of the source generating traffic for
228.9.9.9 which is a private IP address with its own public
address which is 192.168.2.10 , and send it to PPER-WEST.
o The rest of the process of becoming peer C-MAPPERs is as
before, in terms of sending unicast-encapsulated introduction
message to the peer and maintaining connectivity with the
peer by sending introduction messages every 60 seconds as
Keep-Alive messages.
o If any changes occur inside (i.e.) D1 regarding the multicast
sources, PPER-WEST MUST first set the ZTCN-BIT and inform the
change by sending its AMMT to C-MAPPER-EAST.
o Also both PPER-WEST and C-MAPPER-EAST MUST add their domain
number to the domain-set of any multicast source they are
going to advertise to the other one.
2- Sending join/prune message for a multicast group inside a private
PIM-NG domain:
o Considering Figure 46 as our example network, H1 and H2 in
D1 need to receive multicast traffic destined for 228.9.9.9
and 228.6.6.6 which are being originated in D2.
o So H1 starts the process by sending an IGMP message to the
upstream router. And the request will reach CLIENT2.
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o So CLIENT2 starts the process of finding the unicast address
of the source generating traffic destined for 228.9.9.9 by
sending a unicast-encapsulated request to the closest C-RP.
o As the source generating the traffic destined for 228.9.9.9
is using Private IP address within D2, C-MAPPER-EAST had
changed the unicast address of the source with its own
public IP address at the time of advertising to PPER-WEST.
So C-RP will answer to the CLIENT2's request by sending
back the unicast address of the source in the format of (S,
G, domain-set) or (192.168.2.10, 228.9.9.9, 2).
o Client 2 receives the C-RP acknowledge and sends a (S, G,
RPT) join/prune message rooted at the TR to the next hop in
the best path towards the TR.
o TR receives the join/prune message. Clears both the R-BIT
and its address from TR unicast address field and forwards
the message to the next hop in the best path toward the
source of multicast group 228.9.9.9 in D2.
o PPER-EAST receives a join/prune message on its external
interface with the SOURCE UNICAST ADDRESS of 192.168.2.10,
and since PPER-EAST is told that this is the source address
that is used for sources generating multicast traffic
inside its domain (D2) which are using private IP addresses
and not the real address of the source, it knows that some
modifications MUST be done to the message before forwarding
it to the next hop in the best path towards the existing TR
in D2.
o PPER-EAST MUST check the contents of IMST to find the real
unicast address of the source generating traffic destined
to 228.9.9.9, which is 10.2.2.10.
o After finding the real unicast address of the source, PPER-
EAST modifies the join/prune message by changing the source
unicast address inside the message which is 192.168.2.10
with the real address which is 10.2.2.10.
o Since a TR exists inside the domain PPER-EAST MUST set the
R-BIT of source unicast address and put the address of TR
in the appropriate field and forwards the message to the
next hop in the best path towards the TR.
o TR receives the join/prune message and joins the (S, G, RPT)
tree and after clearing both R-BIT and TR unicast address,
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forwards the message to the next hop in the best path
towards 10.2.2.10.
o 10.2.2.10 receives the join/prune message and joins the (S,
G, RPT) tree and starts forwarding the traffic destined for
228.9.9.9 down the tree towards the receiver which is
client2 in D1.
o Now H2 behind client3 in D1 shows interest in receiving
multicast traffic destined for 228.6.6.6.
o Client3 goes through the same process to receive the unicast
address of the source generating traffic for 228.6.6.6. And
after receiving the unicast address which is 192.168.2.50
in the format of (S, G, Domain-set) or (192.168.2.50,
228.6.6.6, 2), goes through the same process as client2 to
send the join/prune message.
o The join/prune message reaches PPER-EAST. Since the source
unicast address is not changed, PPER-EAST MUST forward the
packet to the next hop in the best path towards the
existing TR, without any modifications.
o TR receives the join/prune message and after clearing both
R-BIT and TR unicast address field sends the message to the
next hop in the best path towards 192.168.2.50.
o 192.168.2.50 receives the join/prune message, and joins the
(S, G, RPT) tree and starts forwarding the multicast
traffic destined for 228.6.6.6 down the (S, G, RPT) tree
which is considered to be the SPT towards the receiver in
D1 which is client3.
The above processes are involved in connecting 2 PIM-NG domains in
order to both advertise multicast sources from one private domain to
another and sending join/prune messages from one private domain to
another domain. The related processes were explained through an
example to both simplify the explanation process and understanding
the need for PPER existence in PIM-NG specifications.
In the next sections the concepts regarding PIM-NG-CORE-DOMAIN
through an example will be explained, and after that 2 new concepts
called PIM-NG SUB-DOMAIN and PIM-NG STUB-DOMAIN will be explained and
defined.
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4.6.3. Core-Domain implementation
Up to this point of PIM-NG specifications process explanation, almost
all of the related concepts have been explained. Bellow we are going
to list them to review what has been explained:
o Interaction between a source and C-RP and how a source
registers.
o Interaction between a Client and a C-RP to find a source for a
multicast group (G).
o Interaction between a Client and a source.
o The processes by which the PIM-NG population find the C-RP'(s)
in a multicast domain. And the interaction between C-RP and C-
MAPPER.
o Interaction between TR and C-MAPPER.
o C-MAPPER and C-RP interaction to exchange the information
regarding registered multicast sources in a domain.
o Interaction between C-MAPPERs inside the same domain and
different PIM-NG domains, regarding the exchange of information
related to existing multicast source in each domain.
o Processes involved in connecting multiple PIM-NG multicast
domains.
o . . .
One thing that has remained unexplained is related to a multicast
network design in which PIM-NG-CORE-Domain with TR is considered.
As explained earlier:
o ONLY when a PIM-NG-DOMAIN is connected to the outside network
through a PIM-NG-CORE-DOMAIN
o And ONLY when it is receiving the information regarding
existing multicast sources in other domains through the Core-
Domain, and Core-Domain is consisted of TR'(s).
a client MUST send, its join/prune message for a multicast source
that can be reached through the Core-Domain cloud, first towards the
TR inside to Core-Domain to join the (S,G,RPT) rooted at both any
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existing TR inside client's domain and then the TR inside the Core-
Domain.
The above mechanism will eliminate future join/prune messages for the
same multicast source which might be sent from Clients in other
domains.
So with the above being said, a series of processes will be involved
which are as follows:
o A C-MAPPER'(s) inside a Core-Domain MUST introduce at least one
TR to its peer C-MAPPER in connected PIM-NG-DOMAINs.
o If a CORE-DOMAIN is consisted of more than one TR,PIM-NG
specifications suggests the use of ANYCAST concept, so that the
C-MAPPER'(s) inside the CORE-DOMAIN will only send one unified
TR unicast address to peers in connected PIM-NG-DOMAINs, which
reduces the amount of data being sent in C-MAPPER introduction
message.
o PIM-NG specifications suggests that the unicast address of the
desired TR'(s) to be introduced to peers in PIM-NG-DOMAINs be
dictated to C-MAPPER'(s). This process is actually a MUST as
there might be TRs inside the CORE-DOMAIN cloud that are using
private addresses or must not be introduced to connected PIM-NG-
DOMAINs.
o C-MAPPER'(s) inside the CORE-DOMAIN MUST introduce existing
TR'(s) to peers in PIM-NG-DOMAINs, by sending the unicast
address of the TR'(s) inside the CORE TOPOLOGY TABLE (CTT),
which only contains the information regarding existing TR'(s) in
the CORE-DOMAIN.
o If a PIM-NG-DOMAIN is connected to a PIM-NG-CORE-DOMAIN through
another PIM-NG-DOMAIN, the CTT MUST reach that domain too. For
instance, if D1 is connected to D2 and D2 is connected to CORE-
DOMAIN D10001, then C-MAPPER inside D2 MUST pass the received
CTT to peer C-MAPPER in D1. This process is a MUST if D1 is
receiving information regarding multicast sources in other
domains through D2 and needs to reach outside sources.
o A client in a PIM-NG-DOMAIN in need to receive a multicast
traffic , that the associated DOMAIN-SET shows it can be reached
through a CORE-DOMAIN , MUST use the information regarding the
existing TR'(s) in CORE-DOMAIN at the time of creating
join/prune message . This MUST be done by setting the C-BIT of
source unicast address and putting the address of the CORE-
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DOMAIN-TR in the appropriate field, so that it will reach the TR
inside the CORE-DOMAIN. The logic behind this process will be
explained through an example multicast network.
o After the join/prune message reaches the desired CORE-DOMAIN-
TR, the TR'(s) MUST clear both the C-BIT and information inside
the CORE DOMAIN Tree Root ADDRESS field and then forward the
message to the next hop in the best path towards the source.
Bellow the above processes and the logic behind the above behavior of
PIM-NG specifications at the presence of CORE-DOMAIN-TR will be
explained through an example.
Figure 47 core domain implementation
In the multicast network design illustrated in Figure 47 as an
example we have 2 CORE-DOMAINs with domain numbers 10001 and
10002.D10001 is connected to D1, D2 and D3 and also connected to
D10002, while D10002 is connected to D1.
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A multicast source starts generating multicast traffic destined for
(G) in D1 behind 10002 and the information regarding the source is
passed from C-MAPPER in D1 to C-MAPPER in D10002 as (S, G) with
domain-set (D1). (S, G) is advertised to D10001 by C-MAPPER in D10002
as (S, G) with domain-set (D1, 10002). And finally the information
regarding the multicast source reaches D1, D2 and D3 behind D10001 as
(S, G) with domain-set (D1, 10002, 10001).
As it is illustrated in Figure 47, D3 behind D10001 has direct
unicast connectivity to D1 behind D10002 through a tunnel which is
capable of carrying multicast traffic.
As an example, a client/host in D3 shows interest in receiving
multicast traffic destined for (G) and after receiving the unicast
address of the source generating that traffic, it is going to create
a join/prune message and send it towards the next hop in the best
path towards the source. It is assumed in this example that the best
path is the tunnel interface between D3 and D1. So if the join/prune
message is going to be directed through the tunnel, what happens if
for instance another client in (i.e.) D1 behind D10001 comes up later
and asks to receive the same traffic?. Let's assume that the
join/prune from client in D3 is directed through the tunnel and both
the source in D1 and client in D3 join the SPT for (S, G). Now a new
client in D1 behind D10001 comes up and sends a join/prune message
towards the source in D1 behind D10002, and finally both the source
in D1 and client in D1 behind D10001 join SPT for (S, G). At this
point we see that the source has joined 2 different SPTs to send the
traffic to almost the same destination up to D10001, which is
considered by PIM-NG specifications a waste of resources.
Instead of the above processes , since the domain-set associated with
(S,G) indicates that the update regarding (S,G) passed through CORE-
DOMAIN10001, the client in D3 MUST send its join/prune message in a
way ,so that it will reach the CORE-DOMAIN ,by setting the C-BIT of
the source unicast address filed in join/prune message and putting
the address of the CORE-DOMAIN-TR it had received from the C-MAPPER
in D3 in the appropriate field and then send the message to the next
hop in the best path first towards any existing TR inside D3 and then
after the message reaches the D3-TR and the R-BIT is cleared
towards the CORE-DOMAIN-TR.
This way, as the message reaches the next hop and the next hope sees
that the R-BIT is set in case of existing TR in D3, and also sees
that the C-BIT is set which indicates that the message MUST be first
forwarded towards the CORE-DOMAIN-TR.
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the message reaches the CORE-DOMAIN-TR and the TR clears the C-BIT
and forwards the message to the next hop in the best path towards the
source .and finally the client in D3, the TR in D3, the TR in CORE-
DOMAIN and the source join the (S, G, RPT) rooted at existing TRs in
each domain which is considered the Shortest Path Tree by PIM-NG
specifications, and source starts sending traffic to (G) down the
SPT.
Now if the client in D1 behind D10001 comes up and sends the
join/prune message to receive the same traffic, the join/prune
message will only need to go up to the CORE-DOMAIN-TR, and since the
CORE-DOMAIN-TR has already joined the SPT for (S, G) it will start
forwarding traffic destined for (G) down the SPT towards the client
in D1.
Although the above process may seem unnecessary, it MUST be done to
reduce the amount of join/prune messages that might be sent towards a
source from different domains behind a CORE-DOMAIN and ONLY MUST BE
done whenever the domain-set associated with a multicast source
indicates that it can be reached through a CORE-DOMAIN.
Figure 48 join/prune message being sent towards the source
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4.6.4. Multiple multicast domains scenario
Up to this point of explaining PIM-NG specifications almost all of
the concepts regarding registering a new multicast source, connecting
2 multicast domains, advertising the information regarding a new
multicast source to another domain and many other concepts unique to
PIM-NG have been explained. Now in this section we are going to check
most of the concepts regarding a multicast network consisted of
multiple PIM-NG domains through an example. In Figure 49 a multicast
network consisted of multiple PIM-NG-CORE-DOMAINs and PIM-NG-DOMAINs
is illustrated.
Figure 49 network with multiple multicast domains
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In the illustrated network, you will see 5 PIM-NG-CORE-DOMAINs, 2 of
which connected to some PIM-NG-DOMAINs. we have a PIM-NG-CORE-DOMAIN
which is actually a SERVICE PROVIDER Autonomous System, a transitive
multicast domain which is unique to PIM-NG as the nature of MSDP and
its RPF check method doesn't allow PIM-SM to have a transitive
multicast domain or Autonomous System, an AS which can be considered
an enterprise network that divided its multicast domain in to
multiple PIM-NG-DOMAINs which are all connected to outside world
through the CORE-DOMAIN, and 2 other CORE-DOMAINs that are needed to
make the explanation of RPF check concept and transitory AS/multicast
domain easier.
In Figure 49, the Service Provider network is shown as AS-64500 and
DOMAIN-10001(D10001 from now on) which is a CORE-DOMAIN number, and
is connected to its customer A with PIM-NG-DOMAIN number 1 which is
assigned by the Service Provider to make the customer able of
receiving multicast updates from outside and also send multicast
updates to the outside world. Customer A has divided its network to 2
domains using a private domain number for the second domain. Also the
Service Provider network has another customer connected to it, which
is named Customer B, which is using the SP's network to only connect
its multicast domains and doesn't wish to advertise any multicast
source to the outside world or receive any, and to be more specific
it has a closed and private multicast domain. This D10001 is
connected to another CORE-DOMAIN which is D10002 with AS number
64501.
D10002 is then connected to AS-64502 with DOMAIN number D-10003 which
is assumed to be a transitive AS or multicast domain. D-10003 is only
providing unicast reach ability so that the join/prune messages or
multicast traffic can reach from one domain to other domains. Also
please be noted that this transitive domain can be a PIM-SM domain
which is only providing the unicast reach ability between PIM-NG
domains. It is connected to AS-64503 with Domain number D-10004 and
AS-64504 with Domain number D-10005. D-10004 is only being used to
review the RPF check method used in PIM-NG and D-10005 is considered
to be an organization's Autonomous System which has divided its
multicast domain to multiple domains to have a better control over
its multicast network.
With the above being explained , now it's time to overview the
involved concepts through Figure 50, which shows the network in
Figure 49 but with the multicast sources being advertised from one
domain to other domains.
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Figure 50 multicast network and multicast advertisements
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As illustrated in Figure 50:
o Since customer-B's multicast domain behind D10001 is assumed to
be a private and closed multicast domain, the multicast
sources originated inside its D1 will only be advertised to
D20 which is also customer-B's multicast domain, and will not
be advertised to outside world or better to say to the C-
MAPPER inside D10001. And customer-B is only using multicast
network of D10001 as a mean to exchange multicast traffic
between its multicast domains.
o As it is illustrated in Figure 50, customer-A's multicast
domain is divided in to 2 multicast domains both connected to
D10001 and since customer-A has some sources that needed to be
globally accessible, it has received PIM-NG-DOMAIN number
1(D1) from D10001 (Service Provider). Customer-A uses a
private domain number (D9901) for its second domain, and as it
is illustrated the C-MAPPERs inside D1 and D9901 are directly
connected as a mean to exchange information regarding
multicast sources internally. And D1 is using a PPER to
connect to a C-MAPPER in D10001 in order to exchange
information regarding multicast sources globally/externally.
o A multicast source inside D9901 is originating multicast
traffic destined for (G), and the update about it is
advertised to the peer C-MAPPER in D1 as (S2, G2, D9901). And
since the domain number 9901 is a private domain number, the
PPER in D1 will remove D9901 from the domain-set of (S2,G2)
before advertising it to the C-MAPPER in D10001,and sends the
update as (S2,G2,D1).
o C-MAPPER in D10001 receives the update and advertises it to its
peer in D10002 as (S2, G2, D1, 10001). The C-MAPPER in D10002
is also peer with C-MAPPERs in D10003, D10004 and D10005. As
illustrated in Figure 50, a multicast source (S3) comes up in
D10002 and starts generating traffic destined for (G3). So the
C-MAPPER in D10002 starts advertising information about this
new source too its peers as (S3, G3, D10002).
o D10003 is assumed to be a transitive domain only providing
multicast reachability between D10002, 10004 and 10005. And as
it is illustrated in Figure 50, C-MAPPER in D10002 is only
advertising information about multicast sources that are
generated inside its domain and not those generated in D10001.
This being said, C-MAPPER in D10002 advertises the multicast
source created in its domain as (S3, G3, 10002) to C-MAPPER in
D10003.
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o D10004 and D10005 need to receive the multicast updates
completely, so the C-MAPPER in D10002 peers with C-MAPPER'(s)
or PPER'(s) in D10004 and D10005 and starts sending updates
about multicast sources it knows as (S2,G2,D1,D10001,D10002)
and (S3,G3,D10002) to them.
o Up to this point, C-MAPPER in D10004 and PPER in D10005 as
illustrated in Figure 50 have received the updates. Now the C-
MAPPER in D10004 starts to advertise the received updates to
its peer in D10005. So it advertises them as
(S2,G2,D1,D10001,D10002,D10004) and (S3,G3,D10002,D10004) to
D10005.
o PPER in D10005 receives the updates from its peer in D10004 and
since it has received an update from its peer in D10002, about
the same multicast sources, it starts the RPF check mechanism.
o PPER in D10005, first, compares the DOMAIN-SET of the 2
received updates and the result of the comparison will be
that, the updates received from D10004 will fail the RPF
check. This is due to the fact that the domain set of the
received updates from D10004 are longer than the ones received
from D10002.
o At the end the PPER in D10005 sends the updates to the closest
C-MAPPER inside its domain and the C-MAPPER in D10005
advertises those updates to its peers in D1 and D2.
As explained above, PIM-NG specifications allow the existence of
transitive multicast domain or Autonomous Systems, which due to the
MSDP RPF check nature hasn't been totally implementable.
And also because of the unique RPF check method used by PIM-NG, the
control over filtering the updates about multicast sources is
easier and more enhanced. Which is also mostly because of the RPF
check method used by PIM-NG which allows the existence of
transitory domains or an intermediary multicast domain which only
needs to receive partial updates, like D10003 in Figure 48.
In the following sections, the remaining concepts of PIM-NG
regarding multiple multicast domain connectivity such as SUB-DOMIAN
and PIM-SM-COMPATIBILITY, and controlling the updates received from
a PIM-NG-DOMAIN to improve the security of the multicast network by
STUB-DOMAIN concept will be explained.
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4.6.5. PIM-NG Sub-Domain
PIM-NG Sub-Domain concept is introduced to cover 2 areas:
o To control the propagation of multicast traffic inside one
multicast domain, which from this perspective the Sub-Domain
concept is more like dividing a multicast domain in to different
areas.
o To give the administrators a robust control over a multicast
domain, by dividing it in to different sub-domains. And make
modifications in one sub-domain in a way that no multicast
source updates are accepted from that part of the domain
through using the concept of Stub-Domain, which will be
discussed later, or do FILTEING on the multicast sources that
are usable in a Sub-Domain.
Bellow specifications and rules apply to PIM-NG Sub-Domain:
o A PIM-NG Domain can be divided to up to 254 Sub-domains. This
number is derived from the maximum number of available C-
MAPPERs inside a PIM-NG domain. As said before C-MAPPERs can
have up to 255 different groups and the fact that each C-
MAPPER is already a member of the main PIM-NG domain, gives us
the equation 255-1=254.
o The sub-domain numbers MUST be different from the main domain
number, so that, the C-MAPPER introduction messages meant for
the main domain won't be read by the components of each Sub-
Domain.
o If a PIM-NG domain is divided in to Sub-Domains, all the C-RPs,
TR'(s) and clients resided is a Sub-Domain MUST only be
configured with Sub-Domain number to use it as their domain
number.
o The only components of a PIM-NG domain which MUST be aware of
both the main PIM-NG domain number and the Sub-Domain number
they reside in are C-MAPPERs, PER'(s), PPER'(s) and TR'(s).
o Since the main purpose of dividing a PIM-NG Domain to Sub-
Domains is to have a better control over the propagation of
the information regarding the existing multicast sources, in a
way that either a Sub-Domain doesn't receive the information
regarding specific multicast sources or in a Sub-Domain no
sources are allowed to do exist and send register messages to
C-RPs in the Sub-Domain, any mechanism used such as filtering
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or defining a Sub-Domain as an STUB-Domain, MUST BE applied
within Sub-Domains and at the time the information regarding
multicast sources are advertised within the Sub-Domain to
existing C-RP'(s).
o PIM-NG specification suggests the use of one or more PER'(s) as
the boundary between each 2 Sub-Domain to limit the
propagation of multicast introductions sent by C-MAPPER'(s)
and C-RP'(s) in each Sub-Domain.
o If in a PIM-NG multicast domain , only one C-MAPPER is
considered, then the multicast domain can be divided to ONLY 2
Sub-Domains and the C-MAPPER MUST act as the PER or boundary
between the 2 Sub-Domains with one hand in each Sub-Domain.in
this case the C-MAPPER MUST NOT forward the multicast
introduction messages of one Sub-Domain to the other one.
o If in PIM-NG SUB-DOMAINs, redundancy and high availability of
the C-MAPPERs are needed to be considered, then each SUB-
DOMAIN CAN use as many C-MAPPERs within the Sub-Domain to
support the needs of multicasting in the Sub-Domain But ONLY 2
C-MAPPERs, MUST BE and ARE allowed to be both a member of the
main domain and the Sub-Domain.and the rest of the C-MAPPERs
will only be a member of the Sub-Domain. So if it is not
needed, PIM-NG specifications STRONGLY suggests using 2 C-
MAPPERs in each Sub-Domain.so if redundancy must be considered
the number of Sub-Domains will reduce to 127.
o In the case of redundant C-MAPPERs in each Sub-Domain, the
Mesh-Group concept described in section 4.5.2 MUST BE used
inside each Sub-Domain so only the active C-MAPPER will be
able to send introduction messages destined to 239.0.1.190. so
first C-MAPPERs MUST send their multicast introductions
destined to 239.0.1.188 using the Sub-Domain number, to find
their peers if the dynamic methods are in use and elect the
active C-MAPPER within the Sub-Domain and after that they MUST
send multicast introductions using their main domain number to
find their peers in the main domain if the dynamic methods are
in use.
o As explained in section 4.5.2. , a PIM-NG domain CAN use up to
25 C-MAPPER Mesh-Groups. In this case each 10 C-MAPPER within
either 10 or 5 Sub-Domains, CAN form a C-MAPPER Mesh-Group in
the main domain. for instance, if a PIM-NG multicast domain
with domain number D1, is divided in to 10 Sub-Domains(Sub-
Domain 2-11), with each Sub-Domain including 2 C-MAPPERs for
redundancy and high availability, C-MAPPERs inside Sub-Domains
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2-6 can form Mesh-Group1 in D1 and C-MAPPERs in Sub-Domains 7-
11 can form Mesh-Group2 in D1.
o When a C-MAPPER is a member of the main domain and also a Sub-
Domain, The concept of Active and Standby C-MAPPER in a mesh
group described in section 4.5.2.1. , MUST BE applied to each
Sub-Domain and depending on the needs of the PIM-NG multicast
domain the Active and Standby C-MAPPER concept CAN be applied
in the main domain. So for instance, if D1 is divided into 2
Sub-Domains (Sub-Domain 2-3) with 2 C-MAPPERs in each Sub-
Domain being a member of both the PIM-NG domain and the Sub-
Domain, C-MAPPERs in Sub-Domains2 will form Mesh-Group1 in
Sub-Domain2 and C-MAPPERs in Sub-Domain3 will form Mesh-Group1
in Sub-Domain3. And ALL 4 C-MAPPERs as C-MAPPERs of Domain1
will either form MeSh-Group1 in Domain1 to begin the process
of Active C-MAPPER election in Domain1 between the 4 of them
or simply will become peer C-MAPPERs in Domain1 to exchange
their A-Multicast Mapping Tables and other information needed.
o The Mesh-Groups in the main domain (i.e. D1) are formed to
elect the ACTIVE C-MAPPER ONLY under these circumstances:
1. If a PIM-NG domain which is divided to Sub-Domains, is
connected to outside world or other PIM-NG domains or a
PIM-SM domain by using the PPER concept, and since
PPER'(s) MUST communicate with the closest C-MAPPER in
the PIM-NG domain to receive the full AMMT which is being
exchanged between the C-MAPPERs in the main domain, ONLY
IF the needs of multicast Domain DICTATES TO USE the
dynamic method for the communication of PPER'(s) with C-
MAPPER'(s) in the Domain, then the C-MAPPERs MUST form
Mesh-Group'(s) in the PIM-NG Domain and the active C-
MAPPER MUST ONLY introduce existing C-MAPPERs in the main
domain in its introduction messages sent to 239.0.1.190.
2. If a PIM-NG domain which is divided to Sub-Domains, is
connected to a PIM-SM domain by using the PER concept,
and since in such design PER'(s) MUST communicate with
the closest C-MAPPER in the PIM-NG domain to receive the
full AMMT which is being exchanged between the C-MAPPERs
in the main domain, ONLY IF the needs of multicast Domain
DICTATES TO USE the dynamic method for the communication
of PER'(s) with C-MAPPER'(s) in the Domain, then the C-
MAPPERs MUST form Mesh-Group'(s) in the PIM-NG Domain and
the active C-MAPPER MUST ONLY introduce existing C-
MAPPERs in the main domain in its introduction messages
sent to 239.0.1.190.
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o If Mesh-Group'(s) are formed in the main domain so that through
an election the ACTIVE C-MAPPER starts introducing in the main
domain, then ONLY the PER'(s) acting as the boundary between
Sub-Domains MUST be dictated to pass the introduction messages
sent to 239.0.1.190 which are generated ONLY BY the ACTIVE C-
MAPPER in the main domain and NOT Sub-Domains.
o If a PIM-NG Domain which is divided to Sub-Domains is connected
to other Domains using PPER concept or is connected to a PIM-
SM domain, To reduce the bandwidth and network resources
consumption IF the needs of multicasting in the Domain does
not dictate to use the dynamic methods for the communication
between PPER'(s) or PER'(s) and C-MAPPERs, PIM-NG
specifications Strongly SUGGESTS to statically introduce C-
MAPPER'(s) to each PPER or PER through command initiation on
PPER'(s) and PER'(s).
o If the C-MAPPERs are statically introduced to PER'(s) and
PPER'(s), then a mechanism MUST be used so that the C-MAPPERs
which are member of a Mesh-Group in the main domain, don't
elect the Active C-MAPPER. This way the C-MAPPERs which are
members of the Mesh-Group in the main domain will only
exchange their AMMT'(s) and if needed the information
regarding the existing TR'(s). and Since no Active C-MAPPER is
elected the PER'(s) acting as boundary between the Sub-Domains
MUST NOT be dictated to forward the C-MAPPER introductions
sent to 239.0.1.190 which are generated by the ACTIVE in the
main domain. So PIM-NG specification SUGGESTS doing above
through command initiation as an option.
o Also in case that the C-MAPPER'(s) are introduced to PER'(s) or
PPER'(s) statically, PIM-NG specifications SUGGESTS that the
C-MAPPERs in the main domain simply become peer and don't form
Mesh-Groups, which eliminates the need to use the above
mentioned mechanism.
o With the above concepts, each C-MAPPER within each Mesh-Group
in the main domain, will inform ALL the other members of the
Mesh-Group as soon as any changes occurs within a Sub-Domain.
o If in a PIM-NG Domain divided to Sub-Domains, the C-MAPPERs are
to form Mesh-Group'(s) in the main domain through dynamic
method explained in section 4.5.2. , the PER'(s) acting as the
boundary between Sub-Domains MUST BE dictated to forward the
C-MAPPER introduction messages destined to 239.0.1.188 and
generated ONLY by C-MAPPERs in the main domain. so if Domain1
is divided to Sub-Domains 2 and 3, then the PER'(s) between
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Sub-Domain2 and Sub-Domain3 MUST BE dictated to forward the C-
MAPPER introduction messages destined to 239.0.1.188 with
Domain-Value set to1 (Domain1).
o To reduce the bandwidth and network resources consumption in
the above case, in which C-MAPPERs are to form Mesh-Group'(s)
in the main domain, PIM-NG Specifications Suggests to peer the
C-MAPPERs using the unicast Address of each C-MAPPER and not
the GROUP number of C-MAPPERs which will eventually make the
C-MAPPERs to send multicast introductions to 239.0.1.188 to
find their peers. This being said, the dynamic method is still
the preferred method IF the network infrastructure and
resources can support ALL the needs of PIM-NG multicast
Domain.
o If in the main domain, the C-MAPPER Mesh-Group concept is
implemented with more than one Mesh-Group, then it is advised
to ONLY peer 2 C-MAPPERs from each Mesh-Group with 2 C-MAPPERs
from the other Mesh-Group'(s). The peering of C-MAPPERs inside
different Mesh-Groups formed in the Main domain MUST BE done
using the static method and there MUST be a boundary between
the 2 Mesh-Groups. For instance, if D1 is divided in to 10
Sub-Domains (Sub-Domains 2-11) and C-MAPPERs in Sub-Domains2-6
are forming Mesh-Group1 and C-MAPPERs in Sub-Domains7-11 are
forming Mesh-Group2, then 2 C-MAPPERs from Mesh-Group1 will
become peer with 2 C-MAPPERs in Mesh-Group2 using the static
method to bring redundancy to the entire domain. and it is
STRONGLY advised by PIM-NG specifications to use a PER as the
boundary between Sub-Domains 2-6 and Sun-Domains 7-11 so that
no multicast introduction messages will be forwarded from the
side including Sub-Domains 2-6 to the side including Sub-
Domains 7-11. The above method of connecting different Mesh-
Groups will become necessary in designs with more than 2 Sub-
Domains and many C-MAPPERs in use to reduce the amount of
introduction message traffic in the domain.
o Each Sub-Domain MUST BE treated as a PIM-NG Domain, in which
all the components of the domain including Clients, C-RP'(s),
TR'(s) and C-MAPPER'(s) use the same domain or better to say
Sub-Domain number with the C-MAPPER'(s) and TR'(s) as the only
components being the member of the main domain and Sub-Domain.
So clients, C-RPs and TR'(S) inside a Sub-Domain MUST only
listen to C-MAPPER introduction messages with the same domain
number.
o Since each Sub-Domain MUST BE treated as a separate Domain,
each Sub-Domain can have up to 255 C-RP and TRs if needed, and
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the all the PIM-NG specifications and rules that apply to
exiting C-RP'(s) and TR'(s) in a single multicast domain, are
applicable here.
o C-MAPPERs in a Sub-Domain MUST become peer with other C-MAPPERs
in other Sub-Domains using their main domain number, in order
to advertise the information regarding multicast sources
inside their Sub-Domain to other Sub-domains. So if (i.e.) if
we have C-MAPPER-A and C-MAPPER-B inside D1, and C-MAPPER-A is
a member of sub-Domain-2(SD2) and C-MAPPER-B is a member of
SD-3 , then C-MAPPER-A MUST become peer with C-MAPPER-B which
is inside D1 and not D3.
o As explained in section 4.5.2. ,when there are more than one C-
MAPPER in a PIM-NG domain , each STC-MAPPER MUST send the
information regarding newly found C-RPs or TR'(s) to the
active C-MAPPER in the domain ,so that the active C-MAPPER
will be able to introduce the C-RPs or TRs to the PIM-NG
population by sending introduction messages to 239.0.1.190.
but PIM-NG specifications dictates that in multicast design
including Sub-Domain implementation ,C-MAPPERs MUST NOT send
the information regarding the existing C-RPs in their Sub-
Domain to other C-MAPPERs from different Sub-Domain'(s). And
this is due to the fact that each Sub-Domain MUST BE treated
as a separate Domain. so such information MUST only be
exchanged within the Sub-Domain.
o If TR'(s) are considered in a PIM-NG domain which is divided
into Sub-Domains, since the communication between the TR and a
client is limited to the join/prune messages, then C-MAPPERs
in different Sub-Domains MUST send the information regarding
TR'(s) they find inside their Sub-Domain to their peer C-
MAPPERs which are resided in other Sub-Domains so that :
1. Clients in other Sub-Domains become aware of the
existence of TR and use its unicast address to send the
join/prune message towards the closest TR.
2. TR'(s) will find each other to communicate regarding the
exchange of JOINED-GROUP TABLE.
o In case of existing TR'(s) in a PIM-NG domain divided to Sub-
Domains, PIM-NG specifications STRONGLY suggests :
1. To Use a separate router as the TR if applicable
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2. To Use the ANYCAST concept to introduce the existing TR'(s)
to the clients.
3. NOT TO use C-RP'(s) as the TR if possible, due to the fact
that in this case because of the method used by PIM-NG to
send a join/prune message when C-RP and TR are both the
same, there might be some issues if the C-RPs in one Sub-
Domain go offline and after this the clients in this Sub-
Domain may chose to send their join/prune messages toward an
TR/C-RP resided in another Sub-Domain which doesn't have the
full A-MULTICAST MAPPING TABLE, because of multicast source
filtering in that Sub-Domain.
4. That if the design needs dictates to use C-RP'(s) as TR'(s)
in each Sub-Domain, the TR ANYCAST address used in each Sub-
Domain be different from other Sub-Domains, and C-MAPPERs be
dictated through command initiation as an option NOT TO send
the information regarding the TR'(s) in their Sub-Domain to
other C-MAPPERs which are resided in other Sub-Domains. This
way each single Sub-Domain will totally act as a separate
Domain.
o If more than one TR exists in a PIM-NG Domain which is divided
to Sub-Domains, and the information regarding the TRs is being
exchanged among C-MAPPER so that the clients become aware of
the existence of TR'(s) and also TR'(s) can communicate with
each other using the dynamic method, then TR'(s) MUST use
their main domain number when sending introductions containing
JOINED-GROUPS TABLE to each other and not the SUB-Domain
number, as the only thing that 2 TR CAN share and HAVE in
common is the main domain number.
o TR'(s) MUST introduce themselves to the ACTIVE C-MAPPER in the
Sub-Domain and not an ACTIVE C-MAPPER in the main domain.
o Each C-MAPPER MUST send the information regarding new multicast
sources being originated inside its Sub-Domain to their peer
C-MAPPER'(s) by exchanging the contents of A-MULTICAST MAPPING
TABLE.
o C-MAPPER'(s) that are both a member of a Sub-Domain and the
main domain, MUST remove the Sub-Domain number from the
domain-set of multicast sources inside their Sub-Domain,
before advertising them to their peer C-MAPPER(s)in other Sub-
Domains or outside their multicast domain. After the deletion
of Sub-Domain number, ALL the rules and specifications related
to Domain-Set and RPF check will be applied. This is due to
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the fact that from other C-MAPPERs point of view, whether in
the same PIM-NG domain (i.e. D1) or another PIM-NG domain
(i.e. D2) the updates MUST be seen as generated in D1.
o If any FILTERING in regards to multicast sources needed to be
done, so that a Sub-Domain does not receive the information
regarding an specific multicast source or a group of multicast
sources, it MUST ONLY BE done within each Sub-Domain in a way
that the C-MAPPER'(s) within a Sub-Domain which ARE a member
of the main domain do the filtering on the contents of A-
MULTICAST MAPPING TABLE at the time of advertising to C-
MAPPERs that are only a member of the Sub-Domain or C-RP'(s)
within the Sub-Domain.
o C-MAPPERs in a PIM-NG Domain which is divided to Sub-Domains
MUST exchange the full A-MULTICAST MAPPING TABLE between
themselves without any filtering, and as said above any
filtering MUST ONLY BE done within each Sub-Domain at the time
of advertising to C-RPs within a Sub-Domain. This MUST be done
so that any PER'(s) or PPER'(s) connecting the PIM-NG Domain
to other domain'(s) or PIM-SM domain'(s) receive the full A-
MULTICAST MAPPING TABLE.
o If a PER is placed between 2 PIM-NG Sub-Domains to isolate
them, then the PER MUST know the main domain number it is
resided in. this is a MUST so that where ever the needs of
multicasting dictates the PER will forward the C-MAPPER
introduction messages which are meant to be heard by C-MAPPERs
and PER or PPERs in the main domain.
o If Sub-Domains are isolated from each other by using PER'(s)and
the dynamic C-MAPPER peering methods are used among different
Sub-Domains, then each PER MUST be dictated to let the C-
MAPPER introduction messages destined to 239.0.1.188 and are
meant to finding other C-MAPPER in the main domain ,to be
forwarded from one Sub-domain to the other. As explained
above, up to 2 C-MAPPERs from each Sub-Domain with total
number of 10 C-MAPPERs are allowed to form C-MAPPER Mesh-Group
in the main domain to propagate the information regarding
multicast sources in each Sub-Domain, so it is vital that the
C-MAPPER introduction messages meant for the main Domain are
forwarded by the PER.
o If the C-MAPPERs in existing Sub-Domain have formed more than
one Mesh-Group in the main domain , PIM-NG specifications
STRONGLY suggests that the PER'(s) between the 2 Mesh-Group
areas DO NOT pass the C-MAPPER introduction messages sent to
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239.0.1.188 from one Mesh-Group area to the other. This is
needed to be taken in to consideration when the number of C-
MAPPERs and mesh groups in a multicast domain increase, to
limit the propagation of such traffic. So as explained above
it is STRONGLY suggested to choose at least 2 C-MAPPERs from
each Mesh-Group and make them peer with C-MAPPERs in other
Mesh-Groups using the static methods. consider the bellow
design in which Domain1(D1) is divided in to 4 Sub-
Domains(SD2-5) :
Figure 51 Mesh-Groups and C-MAPPER peering
o If a PIM-NG domain divided to Sub-Domains is connected to a
PIM-SM domain and the 2 domains are separated by a PER which is
acting as the BORDER-PIM-ROUTER(BPR) too, then the PER MUST
become aware of both main PIM-NG domain number and the PIM-NG
Sub-Domain number it resides in, and introduce itself to the
closest C-MAPPER in the main domain if the dynamic method is in
use or to any C-MAPPER that is statically introduced to the PER
using the main domain number and not the Sub-Domain number.
o If a PIM-NG domain is divided to Sub-Domains, and the PIM-NG
domain is connected to other PIM-NG domains using PPER'(s), then
the PPER MUST know both the main domain number and the Sub-
Domain number it is resided in, and MUST automatically
communicate with the closest C-MAPPER in the main Domain and
not the Sub-Domain, if the dynamic method is in use and the
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ACTIVE C-MAPPER within the main domain is chosen to introduce
all existing C-MAPPERs in the PIM-NG domain by sending
introductions destined to 239.0.1.190, or communicate with any
C-MAPPER that is introduced to it in the main domain.
o When a C-MAPPER in a PIM-NG Domain which is divided to Sub-
Domains with multicast source filtering being applied to Sub-
Domains, receives a PER or PPER introduction, it MUST exchange
the full A-MULTICAST MAPPING TABLE with the PER or PPER so that
the PER or PPER has a complete knowledge about existing
multicast sources. This is why such PER or PPER MUST introduce
itself to the C-MAPPERs within the main domain and not the sub-
domain. as explained earlier each Sub-Domain can have as many C-
MAPPERs as needed but only 2 of them are allowed to be a member
of both main domain and Sub-Domain, and if such PER or PPER
introduces itself to the closest C-MAPPER within a Sub-Domain
that multicast source filtering is applied in it, there is a
possibility that the PER or PPER introduces itself to a C-MAPPER
which is only a member of the Sub-Domain and doesn't have the
full A-MULTICAST MAPPING TABLE.
o If a PIM-NG domain is divided to Sub-Domains and the existing
C-MAPPERs within each Sub-Domain are to form C-MAPPER Mesh-Group
with other C-MAPPERs in other Sub-Domains in the main domain
using the dynamic method used by PIM-NG specifications , the
PERs acting as the boundary between Sub-Domains MUST forward the
C-MAPPER introduction messages sent to 239.0.1.188 and
239.0.1.190(active C-MAPPER introduction). This is advised to be
done through command initiation as an option.
o If a PIM-NG domain which is divided to Sub-Domains is connected
to other PIM-NG domains using PPER concept, and the C-MAPPERs in
PIM-NG domain are forming Mesh-Groups then the PERs acting as
the boundary between the Sub-Domains MUST pass the introduction
message of ACTIVE C-MAPPER in the main domain sent to
239.0.1.190, so that the PPER connecting the PIM-NG domain to
other PIM-NG domains will automatically learn the address of the
C-MAPPERs and communicate with them.
o If a PIM-NG domain which is divided to Sub-Domains is connected
to a PIM-SM domain, and the C-MAPPERs in PIM-NG domain are
forming Mesh-Groups then the PERs acting as the boundary between
the Sub-Domains MUST pass the introduction message of ACTIVE C-
MAPPER in the main domain sent to 239.0.1.190, so that the PER
connecting the PIM-NG domain to PIM-SM domain will automatically
learn the address of the C-MAPPERs and communicate with them.
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o If in a PIM-NG Domain which is divided to Sub-Domains and
connected to outside Domains using PPER'(s) or PIM-SM domains
using PER'(s) which act as BPR, more than one C-MAPPER Mesh-
Group is considered , Since it is STRONGLY suggested by PIM-NG
specifications to use a PER between the 2 Mesh-Group area, so
that the ACTIVE C-MAPPER introductions of one area IS NOT
forwarded to other areas, PIM-NG specifications SUGGESTs to
statically introduce at least 2 C-MAPPERs from other Mesh-Groups
that such PER or PPER is not resided in the associated area to
the PER or PPER so that if the connection between the PER or
PPER with the C-MAPPERs inside the closer Mesh-Group area is
lost, the PER or PPERs will be able to communicate with the C-
MAPPERs in other areas.
Figure 52 PPER and PER communication with C-MAPPER
As explained above throughout different rules and specifications that
apply to PIM-NG Sub-Domain'(s), the Sub-Domain concept is introduced
to give administrators and designers the ability to divide the
multicast domain to different areas and provide a robust control over
the propagation or advertisement of the multicast sources within each
area or better to say Sub-Domain or as a security feature treat a
Sub-Domain in a way that no multicast source registration is allowed
in an specific area or Sub-Domain by applying the STUB-DOMAIN concept
to that Sub-Domain . In Figure 53 a PIM-NG domain divided to Sub-
Domains is illustrated.
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Figure 53 Sample PIM-NG domain Divided to Sub-Domains
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4.6.6. PIM-NG Stub-Domain
PIM-NG introduces the STUB-DOMAIN concept as a security feature when
dealing with multiple PIM-NG Domains or PIM-NG Sub-Domains. Through
implementing the STUB-DOMAIN concept, a PIM-NG Domain or Sub-Domain
is treated as a multicast domain in which only receivers for
multicast traffic exist.
The bellow specifications and rules apply to a PIM-NG STUB-DOMAIN:
o A STUB-DOMAIN is a domain in which, no multicast source exists.
o A STUB-DOMAIN is a domain in which, ONLY multicast traffic
receivers MUST exist.
o If a Domain is considered to be STUB-DOMAIN, the C-RP'(s)
within the Domain MUST BE dictated NOT TO accept any source
register messages. To do so PIM-NG specifications Suggests that,
at the time of configuring the domain number in which a C-RP
exists, the C-RP be dictated that the domain it is resided in is
a STUB-DOMAIN.
o If a Domain is considered to be a STUB-DOMAIN, the C-MAPPERs
inside the Domain MUST BE dictated NOT TO accept any multicast
source advertisement from existing C-RP'(s), or better to say
the C-MAPPER'(s) inside a STUB-DOMAIN MUST NOT receive any AMMT
from the C-RP'(s) inside the domain, and if any A-MULTICAST
MAPPING TABLE is received from C-RP'(s) it MUST NOT be accepted.
o If a PIM-NG Domain is divided to PIM-NG Sub-Domains, and one or
more Sub-Domain'(s) MUST be treated as a STUB-DOMAIN, then ALL
C-RP'(s) inside such Sub-Domain'(s) MUST become aware about the
situation, so that they WILL NOT accept any source register
messages.
o If a PIM-NG Domain is divided to PIM-NG Sub-Domains, and one or
more Sub-Domain'(s) MUST be treated as a STUB-DOMAIN, then C-
MAPPER'(s) inside such Sub-Domain'(s) MUST NOT accept any AMMT
from the C-RP'(s) inside the Sub-Domain.
o If 2 separate PIM-NG multicast domains (i.e. D1 and D2) are
connected and one of them (i.e. D1) is considered by the other
Domain (i.e. D2) a STUB-DOMAIN, then the C-MAPPER'(s) or
PPER'(s) in the Domain which is not a Stub-Domain (i.e. D2) MUST
NOT accept any multicast source advertisements from the peer C-
MAPPERs in the Domain that is considered a STUB-DOMAIN (i.e.
D1). PIM-NG specifications suggests that this be done at the
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time of introducing the peer C-MAPPERs.for instance by
initiating a command like this :
o No AMMT MUST BE received or accepted from a peer C-MAPPER which
is considered to be in a STUB-DOMAIN.
o The C-RP'(s) inside a STUB-DOMAIN MUST only receive AMMT from
C-MAPPER'(s) in the domain and MUST NOT generate any AMMT.
o Since as dictated by PIM-NG specifications NO advertisements
regarding multicast sources can be accepted from a STUB-DOMAIN,
In a multicast network design with a STUB-DOMAIN in the middle
of 2 normal domains PIM-NG specifications suggest 2 different
approaches:
1. If possible, C-MAPPER'(s) from the normal Domains MUST
become peer with each other and also the C-MAPPER'(s) in
the STUB-DOMAIN, so that the C-MAPPER'(s) in the normal
Domains can exchange information regarding multicast
sources originated in their domains and only advertise
them to the C-MAPPER'(s) in the middle domain. in this
method the STUB-DOMAIN acts as a transitory multicast
domain and actually is used by the normal domains as a
path to send join/prune messages and receive the desired
multicast traffic.
2. If it is not possible to make the C-MAPPERs in normal
domains peer with each other, PIM-NG specifications
suggest to use a mechanism as an optional feature in
regards to STUB-DOMAIN, so that the C-MAPPER'(s) in
normal domains become peer with the C-MAPPER'(s) in the
STUB-DOMAIN and accept receiving advertisements
regarding multicast sources or better to say accept the
received AMMT from C-MAPPER'(s) in the STUB-DOMAIN, BUT
filter any information regarding multicast sources that
are generated within the STUB-DOMAIN.
o The above approach is unique to PIM-NG because of its unique
RPF check method, which allows the existence of transitory
multicast domains or Autonomous Systems. The above
explanations can be seen in Figure 54.
o If a PIM-NG domain is connected to a PIM-SM domain, and the
PIM-SM domain is considered to be a STUB-DOMAIN, PIM-NG
specifications follows 2 different approaches:
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1. If the PIM-SM domain is between 2 PIM-NG domains, the
C-MAPPER'(s) which is becoming MSDP-PEER with RP'(s) in
the PIM-SM domain MUST BE dictated not to accept any
Source Active messages from their MSDP-PEER'(s). And C-
MAPPERs within the PIM-NG domains MUST become peer with
each other.
2. if the PIM-NG domain is connected to a network of PIM-
SM domains and the directly connected PIM-SM domain must
be considered a STUB-DOMAIN, the C-MAPPER'(s) in the
PIM-NG domain MUST be dictated as an optional feature to
perform filtering on the received Source Active messages
received from the MSDP-PEER in the STUB-DOMAIN, so that
any source with the originator address equal to the
address of the MSDP-PEER is filtered.
Figure 54 Stub-Domain as the transitory multicast domain
The above specifications and rules apply to a PIM-NG STUB-DOMAIN. and
the reason that the Stub-Domain concept is explained as a part of the
concepts related to PIM-NG and multiple multicast domains, is that
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this concept is only meaningful and applicable when we are dealing
with multiple multicast domains, and the STUB-DOMAIN concept can be
used as a security measure when dealing with multicast domains that
no multicast source'(s) are expected to be advertised from them, to
eliminate the possibility of existing attackers.
4.7. PIM-SM compatibility
Up to this point of explaining different concepts of PIM-NG as a new
multicast protocol, almost ALL aspects of PIM-NG specifications have
been covered.
Now it is time to make it compatible with its predecessor PIM-SM, so
that PIM-NG multicast domains can be connected to PIM-SM domains or a
network of PIM-SM domains. Compatibility of PIM-NG with PIM-SM is
related to the bellow fields:
o Exchanging the information regarding the multicast sources
originated in either the PIM-NG Domain'(s) or PIM-SM Domain'(s),
so that receivers can find the source for their desired
multicast traffic and send join/prune messages towards the
desired multicast source, whether it is inside a PIM-NG Domain
or PIM-SM Domain.
o The transformation of PIM-NG join/prune messages to PIM-SM
messages so that routers that are only PIM-SM aware will be able
to forward the join/prune messages to the final destination.
o The transformation of PIM-SM join/prune messages to PIM-NG
join/prune messages so that the join/prune message can be
forwarded according to PIM-NG specifications within the network
of PIM-NG Domains.
In the following sections, different concepts, specifications and
rules in regards to connecting a PIM-NG multicast domain to a PIM-SM
multicast domain will be discussed. First the concepts regarding the
exchange of information regarding originated multicast sources in the
form of Source Active (SA) messages will be discussed and after that
the concepts related to sending join/prune messages will be
discussed.
4.7.1. PIM-SM compatibility and SA messages
As described by RFC 3610[9], the information regarding originated
multicast sources MUST be exchanged between RPs that are MSDP peer.
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And such information is sent from one RP to another RP, in a Source
Active (SA) message, which contains:
o Originator address or the unicast address of the originating RP
o Source address or the unicast address of the source generating
the traffic
o Group address the source sends data to
And In PIM-NG as described in section 4.5. , the information
regarding newly originated multicast sources is carried inside AMMT
and between peer C-MAPPERs using unicast-encapsulated C-MAPPER
introductions, which contains:
o Originator address or the unicast address of the originating RP
o Source address or the unicast address of the source generating
the traffic
o Group address the source sends data to
o Domain-Set
As it has been described, the format of AMMT and the information
related to newly originated multicast sources is similar to the
contents of SA messages used by PIM-SM MSDP peers, which makes it
easier to connect a PIM-NG Domain or a network of PIM-NG multicast
domains to a PIM-SM Domain or a network of PIM-SM multicast Domains.
And by connecting in this section PIM-NG specifications refers to the
exchange of information regarding multicast sources.
The rules, concepts and specifications regarding compatibility of
PIM-NG and PIM-SM are as follows:
o Depending on whether we are dealing with a public or private
PIM-NG domain, a C-MAPPER or PPER in the PIM-NG Domain MUST BE
chosen to become MSDP-PEER with an RP in the PIM-SM Domain.
o All the rules that apply to MSDP [9] MUST be applied when a C-
MAPPER or PPER becomes MSDP-PEER with an RP.
o Whenever a C-MAPPER which is also MSDP-PEER with an RP,
receives an update regarding newly originated multicast sources
inside the AMMT from a PEER C-MAPPER and needs to advertise the
received update to the MSDP-PEER'(s):
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1. It MUST remove the DOMAIN-SET of any multicast sources
that are to be advertised to the MSDP-PEER'(s)
2. It MUST create a Source Active message containing
information regarding ALL multicast sources that are to be
advertised to the MSDP-PEER'(s).
3. The SA message contains ONLY:
o Originator address
o Source unicast address
o Group destination
Which is exactly what an SA carries.
o Then the C-MAPPER MUST send the SA message to its MSDP-PEER'(s)
the way explained by MSDP specifications [9] to bring
compatibility to PIM-SM.
o Because of the RPF method used by MSDP, the C-MAPPER or PPER
which is becoming MSDP-PEER with an RP MUST reside in the first
Autonomous System in the best path towards the AS in which the
originator C-MAPPER exists.
o As explained by PIM-NG specifications, each multicast source
has a Domain-Set associated with it, which shows that in which
domain a source is being originated and also is used for PIM-NG
RPF check. So when a C-MAPPER receives an SA message from a
MSDP-PEER (RP), and needs to advertise the information to a PEER
C-MAPPER, it MUST add the following to the Domain-Set:
1. Its own domain number
2. A value equal to letter "S" which shows that this source
is received from a network of PIM-SM Domain'(s). So if C-
MAPPER in Domain1 receives an update for (S, G) from its
MSDP-PEER, and needs to update it to its PEER C-MAPPER'(s),
it MUST modify the Domain-Set as explained and advertise
the associated Domain-set as (D S, 1).
o If a C-MAPPER receives an update for (S,G) from a MSDP-PEER,
and an update for the same (S,G) from a peer C-MAPPER which the
associated Domain-Set indicates that (S,G) is originated inside
a PIM-NG Domain and not a PIM-SM domain, then the update
received from the peer C-MAPPER MUST pass the RPF check.
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o If a C-MAPPER receives an update for (S,G) from a MSDP-PEER,
and an update for the same (S,G) from a peer C-MAPPER which the
associated Domain-Set indicates that (S,G) is originated inside
a PIM-SM Domain and not a PIM-NG domain, then the update
received from the MSDP-PEER MUST pass the RPF check.
o If a C-MAPPER receives an update from a peer C-MAPPER regarding
sources that MUST be considered as SUSPENDED, the C-MAPPER MUST
NOT send any SA message to MSDP-PEER'(s) until the suspension
time is over and the multicast sources are either deleted or
active again.
o If a C-MAPPER loses its connectivity with its MSDP-PEER, it
MUST start the suspension timer and send an update about the
suspended multicast sources to peer C-MAPPER, and if after the
suspension duration which defaults to 5 minutes, the connection
with the MSDP-PEER is not established again, it MUST delete the
received multicast sources from that MSPD-PEER and inform peer
C-MAPPER'(s).or if it has been receiving updates regarding those
sources from a peer C-MAPPER or MSDP-PEER it MUST put the
received updates from those peers in it's a-MULTICAST MAPPING
TABLE and inform its PEER'(s).
o .
4.7.2. PIM-SM compatibility and join/prune messages
A PIM-NG multicast Domain is connected to a PIM-SM multicast Domain,
using a PER or PPER to isolate the 2 multicast Domains and prevent
the propagation of multicast introduction messages of PIM-NG Domain
in to PIM-SM Domain and also to prevent the propagation of PIM-SM
multicast traffic related to BSR[9] and RP'(s) within the PIM-SM
domain.
As mentioned in different parts of PIM-NG specifications, a PER or
PPER which acts as boundary between a PIM-NG Multicast Domain and a
PIM-SM Multicast Domain is called a BORDER-PIM-ROUTER(BPR). And the
responsibility of exchanging join/prune messages between the 2
Domains is on the BPR. But due to the fact that PIM-NG uses its own
version of join/prune message which is different from that of PIM-SM
in parts related to the Tree Root UNICAST ADDRESS, a BPR MUST modify
the join/prune messages received from a PIM-SM Domain and likewise it
MUST do the same when forwarding join/prune messages from a PIM-NG
Domain to a PIM-SM Domain.
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Bellow specifications, concepts and rules apply when a join/prune
message is forwarded from a PIM-NG domain to a PIM-SM domain and
likewise from a PIM-SM Domain to a PIM-NG Domain:
o If a PER is chosen to act as a BPR, then as soon as the PER is
configured and becomes aware that it is connected to a PIM-SM
Multicast Domain, it MUST introduce itself to the closest C-
MAPPER within the PIM-NG Multicast Domain. The BPR introduction
is done by the PER and through sending a unicast-encapsulated
introduction message (4.6.1.2. ) to the closest C-MAPPER or any
C-MAPPER that is introduced to the PER. The type of the
introduction message is set to BPR, and the B-BIT in the
introduction message MUST BE set which indicates to the
receiving C-MAPPER that it's Domain is connected to a PIM-SM
Domain and it MUST start sending the full AMMT to the PER.
o If a PPER is chosen to act as BPR the introduction process as
the BPR is not needed due to the fact that the PPER MUST
introduce itself to the closest C-MAPPER or any C-MAPPER that is
introduced to it as soon as it is configured to be a PPER.
o A BPR has 2 types of interfaces:
1. Internal: an internal interface is connected to the PIM-
NG Domain.
2. External: an external interface is connected to the PIM-
SM Domain.
o A BPR MUST convert any PIM-NG join/prune messages for (S,G) it
receives from within the PIM-NG Domain or better to say on an
internal interface to a PIM-SM join/prune message, before
forwarding it on an external interface which is connected to a
PIM-SM Domain. The conversion process is not time consuming, due
to the fact that the PIM-NG join/prune messages are designed to
be similar to PIM-SM join/prune messages as much as possible.
o A BPR MUST convert the join/prune messages it receives on an
external interface connected to a PIM-SM Domain, ONLY under
these conditions:
1. At least one TR MUST do exist in the PIM-NG Domain.
2. If no TR exists inside the PIM-NG Domain, then For each
(S,G) in the join/prune message, the BPR MUST first check
it's AMMT which it receives from the C-MAPPER'(s) inside
the PIM-NG Domain. And ONLY IF:
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o It finds an entry inside the AMMT for the (S,G).
o The Domain-Set associated with the (S, G) indicates
that the (S, G) is reachable via a connected PIM-NG-
CORE-DOMAIN, or better to say the update regarding
the (S,G) is passed through a PIM-NG-CORE-DOMAIN.
The BPR MUST convert the PIM-SM join/prune message to PIM-NG
join/prune message, and fill out the required fields related
to the TR UNICAST ADDRESS and CORE TR UNICAST ADDRESS.
o If none of the above conditions are meat, PIM-NG specifications
STRONGLY ADVISES that the BPR DO NOT convert the PIM-SM
join/prune message and only forward it to the next hop in the
best path towards the source.
o The above being said, ALL PIM-NG-AWARE routers MUST BE PIM-SM
Compatible in parts mostly related to forwarding join/prune
messages.
o if a BPR receives a join/prune message for (G) on an external
interface connected to PIM-SM with the S-BIT of SOURCE UNICAST
ADDRESS being set, which means that the join/prune is a PIM
version 1 type of message it MUST NOT convert the PIM-SM
join/prune to PIM-NG join/prune.
4.8. Loop prevention
In order to have a loop free multicast domain PIM-NG suggest the use
of Reverse Path Forwarding check(RPF)to prevent any loops from
occurring.
Such loops can be under one of the bellow categories:
o C-MAPPER multicast introduction or notification messages
destined to 239.0.1.190 and sent to ALL-PIM-NG-AWARE routers
within a multicast domain.
o C-MAPPER multicast introductions destined to 239.0.1.188 which
is used by existing C-MAPPER'(s) to find either a backup or peer
C-MAPPER.
o C-RP multicast introductions destined to 239.0.1.189 which is
used by existing C-RP'(s) to find either a backup or peer C-RP.
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o Loops occurring due to a join/prune message which is sent hop
by hop towards an existing source by a client which needs to
join the SPT for (S, G) in scenarios which clients are connected
to each other through switches and within a LAN.
To eliminate and prevent such loops PIM-NG uses the RPF check method
and concept used by PIM-SM which is the best current practice. And
since no shared tree (*, G, rpt) rooted at RP forms in PIM-NG there
won't be any need for such RPF check although since PIM-NG-AWARE
routers are by default PIM-SM compatible it MUST be considered.
The bellow rules MUST be applied to prevent any loops by the unwanted
propagation of such multicast introductions:
o PIM-NG boundary routers such as PER, PPER, BPR or EDGE-
CLIENT'(S) MUST NOT forward such introduction messages to
other domain'(s) in case of PER, PPER and BPR and down the
MULTI-ACCESS network in case of EDGE-CLIENT'(S).
o C-MAPPER'(S) which receive an introduction message destined to
either 239.0.1.190 or 239.0.1.188 with the source address
being equal to C-MAPPER'(s) address MUST discard the packet
and NOT forward any further.
o C-RP'(S) which receive an introduction message destined to
either 239.0.1.189 with the source address being equal to C-
MAPPER'(s) address MUST discard the packet and NOT forward any
further.
4.9. DR election and PIM Assert Message
PIM-NG specifications suggest using the processes and concepts
introduced and defined by PIM-SM [7] with regards to Assert messages
and DR election as the best current practice when dealing with
scenarios and topologies involving multi-access LAN'(s).
The only place that the DR election is different from that of PIM-SM
is in implementations and topologies in which EDGE-CLIENT'(s) are
considered at the edge of a multi-access network which allows the
administrators to dictate the DR for the Multi-Access network by
manipulating the priority of Edge-Clients. So the Edge-Client with
higher priority becomes the DR for the entire Multi-Access network.
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5. Security Considerations
This section is going to cover some of the security concerns related
to PIM-NG specifications covered in this document, and possible
solutions for those security issues. As this document is an earlier
version of PIM-NG specifications, only related security issues are
going to be covered.
5.1. Attacks based on forged messages
The extent of possible damages depends on the type of messages that
are forged. PIM-NG processes use different kinds of messages like
link-local messages, multicast messages and unicast messages. And
each type of message will be discussed separately.
5.1.1. Unicast forged messages
As Register, join and leave messages alongside C-RP introduction
messages sent to C-MAPPER are forwarded by intermediate routers to
their destination using normal IP forwarding, without authentication
there is a high possibility for an attacker anywhere inside the
network, to forge these messages .the effects of such forgery can be
as follows:
1- By forging a register message an attacker can inject forged
traffic into the RP and to the entire PIM-NG domain.
2- By forging join message ,an attacker may become able to act as the
man in the middle and receive a traffic that is not meant for that
receiver .or traffic can be delivered to parts of the network that
no legitimate receivers exists ,which can cause waste of bandwidth.
3- By forging leave message, an attacker can prevent a legitimate
receiver from receiving the traffic it needs.
4- By forging a C-RP introduction message sent to the C-MAPPER, an
attacker can become a real threat to the entire domain, by
injecting false information to the domain.
5- By forging a TR introduction message sent to C-MAPPER, an attacker
can become a real threat to the domain, by becoming a man in the
middle and receive a copy of all the multicast traffic that is
passing through the TR or by dropping the received join/prunes
which can cause the connectivity problems.
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5.1.2. Forged link local messages
As Forged Hello messages are sent to link-local ALL-PIM-ROUTERS and
are not forwarded by the compliant router, they can cause problems
such as:
1- If the source of forged message is inside a Multi-access LAN or to
be more specific a local client, it can give an attacker the
possibility of playing the role of an EDGE-CLIENT, and prevent the
legitimate receivers from receiving the desired traffic or reaching
the desired sources.
2- By forging a Hello message an unauthorized client may become able
to play the role of designated router (DR) for a LAN and become
responsible for forwarding traffic on behalf of local members or
hosts. This can prevent hosts from receiving the desired traffic.
3- By forging a Hello message, an unauthorized router in a PIM-NG
domain can become part of the domain and cause damages such as
preventing its neighbors from receiving C-MAPPER introductions or
injecting false information inside the PIM domain topology table.
5.1.3. Forged multicast messages
C-MAPPER introduction messages sent to ALL-PIM-NG clients , MAPPER
introduction messages sent to ALL-PIM-NG-MAPPERs in order to finding
the PEER-C_MAPPERs or SC-MAPPERs and C-RP introduction messages sent
to ALL-PIM-NG-RPs are PIM-NG multicast messages required for the
processes of PIM-NG. But an attacker might become able to forge such
messages and cause damages. The damages that can be done to a PIM-NG
domain are as follows:
1- By forging a C-MAPPER introduction message sent to ALL-PIM-NG-
CLIENTS (239.0.1.190), an attacker can inject false information in
to the domain, by either injecting false data into the PIM domain
topology table.
2- By forging a C-MAPPER introduction message sent to ALL-PIM-NG-
CLIENTS, an attacker can take the role of C-MAPPER and introduce
itself to C-RPs and finally , can cause the clients not to be able
to find the existing C-RPs , and prevent them from receiving the
desired traffic.
3- By forging MAPPER introduction message sent to ALL-PIM-MAPPERs ,an
attacker can become able to take the role of ACTIVE C-MAPPER in the
process of ACTIVE-C-MAPPER election, and also become peer with
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other C-MAPPER'(s) and cause damage to the domain by injecting
false data into the A-MULTCAST MAPPING table.
4- By forging RP introduction message sent to ALL-PIM-RPs, an
attacker can be able to take the role of C-RP in the process of C-
RP election or become the ACTIVE C-RP in a C-RP Mesh-Group and also
become peer with other existing C-RP'(s) in search of its peer and
cause problems by injecting false data in to either MULTICAST
MAPPING table or A-MULTICAST MAPPING TABLE. And preventing
legitimate receivers from receiving the desired traffic.
5.2. Non-cryptographic authentication mechanisms
A PIM-NG router should provide an option to limit the set of
neighbors from which it accepts join/prune, Assert, and hello
messages, by either static configuration of IP addresses or an IPSEC
security association CAN be used. And a PIM-NG router should not
accept protocol messages from a router from which it has not yet
received a valid hello message. Also a PIM-NG router SHOULD NOT
accept any hello message from a router that is not within the same
PIM-NG Domain unless it is a PIM-EDGE-ROUTER acting as the boundary
between different PIM-NG Domains.
A Designated Router MUST NOT register-encapsulate a packet and send
it to the C-RP if the source address of the packet is not a legal
address for the subnet on which the packet was received. Similarly, a
PIM EDGE-CLIENT MUST NOT accept a register message from its
downstream PIM-NG Clients, if the source address of the register
message is not a legal address for the subnet on which the register
message is received.
A Designated Router MUST NOT accept a C-RP acknowledge packet whose
IP source address is not a valid C-RP address for the local Domain.
Similarly, a PIM EDGE-CLIENT MUST NOT accept a C-RP acknowledge
packet whose IP source address is not a valid C-RP address for the
local Domain.
A mechanism MUST be considered as an option so that a C-RP restricts
the range of source addresses from which it accepts Register-
Encapsulated packets. Also it is STRONGLY advised to consider a
mechanism through which a C-RP restricts the range of source
addresses from which it accepts C-MAPPER or C-RP introduction
messages, so that a possible attacker cannot send such messages or
such messages from unknown ranges are not accepted. Also as explained
throughout PIM-NG specifications a C-RP MUST NOT accept source
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register, C-RP, C-MAPPER messages with different Domain number from
the one dictated to the C-RP.
A mechanism MUST be considered as an option so that a C-MAPPER
restricts the range of source addresses from which it accepts
unicast-encapsulated C-MAPPER, C-RP, PER, PPER, and TR messages
within the same Domain, due to the fact that if dynamic methods
explained by PIM-NG specifications are used if this ranges are not
restricted an attacker may try to introduce itself to the C-MAPPER as
a legitimate component of a PIM-NG Domain. As explained throughout
the PIM-NG specifications, a C-MAPPER MUST ONLY accept C-RP, TR, PER
and PPER introduction messages that carry the same Domain number as
the Domain number dictated to the C-MAPPER.
All options that restrict the range of addresses from which packets
are accepted MUST default to allowing all packets.
5.3. Authentication
Like PIM-SM [7], PIM-NG specifications recommends to use IPSEC [4]
transport mode using the Authentication Header (AH) to prevent the
above attacks against PIM.
The proposed methods of protecting:
o Link-Local Multicast Messages
o Unicast register messages
By PIM-NG, are the methods recommended by PIM-SM Specifications [7]
as the best current method of protecting the above PIM messages.
Since PIM-NG uses processes different from that of PIM-SM in parts
related to:
o The unicast C-RP acknowledge to the DR instead of sending
register stop message.
o Unicast introduction messages, sent from C-RP to C-MAPPER.
o Unicast introduction messages, sent between the C-RPs.
o Unicast introduction messages, sent between the C-MAPPERs.
o Unicast introduction messages, sent from BPR, PPER, and any
existing TR to C-MAPPER.
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o Unicast introduction messages, sent between existing TRs.
a mechanism MUST BE taken in to consideration to protect such
messages.
With the above being said, PIM-NG recommends to use, the Register
Message protection method and Register-Stop protection mechanism
recommended by PIM-SM[7] which is considered the best current method
of protecting unicast Messages.
5.3.1. Protecting Multicast Introduction Message
One important security threat to a PIM Domain that is not covered is
related to the multicast messages sent from a C-MAPPER to all PIM-NG
routers which is similar to the process related to BSR[9]. since when
in a PIM Domain the dynamic methods of finding RP (PIM-SM), C-RP
(PIM-NG) are in use, the multicast messages sent from a C-MAPPER or
BSR play the main role in the process of introducing existing C-RP or
RP to all PIM-NG or PIM-SM routers, a mechanism MUST be taken in to
consideration so that a PIM-NG CLIENT or simply put a PIM router
doesn't accept an unauthorized C-MAPPER introduction message.
in order to protect such a message, PIM-NG recommends that an SA and
SPI be defined on existing legitimate C-MAPPERs and on all PIM-NG
routers by the network administrator to authenticate such multicast
messages. So if an unauthorized C-MAPPER multicast introduction
message is received by the first PIM-NG-AWARE router, it will be
rejected (dropped without process) and won't be forwarded any
further.
5.4. Denial-Of-Service attacks
There are number of denial-of-service attacks against PIM-NG that can
be caused by generating false PIM-NG protocol messages or false
traffic. Using the authentication methods can prevent some, but not
all, of these attacks. Some of the most possible attacks are:
o Sending packets to many different group addresses quickly can
be considered a denial-of-attack, which can cause many register
packets, loading the DR, the C-RP, the C-MAPPERs when more than
one C-MAPPER exists and finally the routers between these
components.
o Many forged join messages can cause many multicast trees to be
set up and consume network resources.
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o With regards to PIM-NG, many forged join messages can cause
many Request For Source messages that will be sent from a CLIENT
to the C-RP, and can be considered a denial of service attack.
To reduce the possibility of the creation of unwanted register
messages, if applicable, PIM-NG specifications STRONGLY suggest using
the STUB-DOMAIN concept (4.5.6) in Domains that no multicast source
is supposed to exist.
6. IANA Considerations
6.1. PIM-NG multicast destination group addresses
PIM-NG processes require to use 3 multicast addresses from the
internetwork control block (RFC 5771[2]).for the simplicity of
explanation process in this documents these 3 addresses are chosen
from the scoped multicast ranges. The addresses are needed for the
bellow processes:
o Destination group address used for C-MAPPER introduction
process. The multicast introduction message is sent to ALL-PIM-
NG routers.
o Destination group address used for C-MAPPER introduction
process so that C-MAPPERs can find each other dynamically. The
multicast introduction message is sent to ALL-PIM-NG C-MAPPERs.
o Destination group address used for C-RP introduction process so
that C-RPs can find each other dynamically. The multicast
introduction message is sent to ALL-PIM-NG C-RPs.
These addresses are needed to be assigned by IANA after this document
is approved.
6.2. PIM-NG packets and values of type field
New type values in PIM-NG packet header and new packet formats
designed specifically for PIM-NG to support the needs of the
different processes of PIM-NG, and will need to be reviewed by the
experts and assignments need to be made.
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6.3. PIM-NG Domain numbers
The PIM-NG Domain number field is considered as a 32 bit field to
support the future needs of multicasting, in regards to PIM-NG
Multicast Protocol.
Domain Number (4.6.1.1) has a vital role in PIM-NG processes and
functionality, which provides the possibility of using Sub-Domain
concept as a security feature. Also it MUST BE noted that through
using the Domain numbers, PIM-NG is able to use a unique RPF method
and a simple multicast domain isolation and separation method, which
provides many features in comparison to the previous versions of PIM
protocol.
CORE-DOMAIN assignments are needed to be done by IANA as the
controlling entity, so that, no conflict can happen as explained
throughout this document.
7. Conclusions
PIM-NG is a multicast protocol that , although may seem to have lots
of features compared to previous protocols like PIM-SM, but through
its many features and processes, provides a robust and sound control
over the propagation of the information regarding the existing
multicast sources. Its processes are enhanced, so that a host in
search of the source of a multicast traffic can communicate with the
desired source as fast as possible, by eliminating the need to
necessarily join the RPT rooted at an RP within a multicast domain.
Also duo to its unique method of RPF check provides the ability of
implementing transitory multicast domains which was not implementable
before. And because of using the Domain concept provides many
features in parts related to security and controlling over the
propagation of multicast information inside a PIM-NG multicast
Domain.
8. References
8.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
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[2] Cotton, M., L. Vegoda and D. Meyer, "IANA Guidelines for IPV4
Multicast Address Assignments", RFC 5771, March 2010.
[3] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, version 3",
RFC 3376, October 2002.
[4] Kent, S. and K. Seo, "Security Architecture for the Internet
Protocol", RFC 4301, December 2005.
[5] Narten, T. and H. Alvetrand, "Guildlines for Writing an IANA
considerations section in RFCs", BCP 26, RFC 5226, May 2008.
[6] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP",
RFC 4607, August 2006.
8.2. Informative References
[7] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
[8] Fenner, B. and D. Meyer, "Multicast Source Discovery
Protocol (MSDP)", RFC 3618, October 2003.
[9] Bhaskar, N., Gall, A., Lingard, J., and S. Venaas, "Bootstrap
Router (BSR) Mechanism for PIM Sparse Mode", Work in Progress,
May 2006.
[10] Hardjono, T. and B. Weis, "The Multicast Group Security
Architecture", RFC 3740, March 2004.
[11] Kim, D., Meyer, D., Kilmer, H., and D. Farinacci, "Anycast
Rendezvous Point (RP) mechanism using Protocol Independent
Multicast (PIM) and Multicast Source Discovery Protocol
(MSDP)", RFC 3446, January 2003.
[12] Savola, P., Lehtonen, R., and D. Meyer, "Protocol Independent
Multicast - Sparse Mode (PIM-SM) Multicast Routing Security
Issues and Enhancements", RFC 4609, August 2006.
9. Acknowledgments
The author would like to thank Mr.Reza Izadi for his review and kind
comments, corrections and support throughout the process of designing
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and writing different concepts of PIM-NG Multicast Protocol. Also the
author would like to thank Mr.Stig Venas for his review and comments
which helped to make this draft complete.
This document was prepared using 2-Word-v2.0.template.dot.
Authors' Addresses
Saeed Sami
P.O.BOX 1466955316
Sanat. SQ
Darya.Blvd
Shafagh.st
Tehran. Iran
Phone: +989123844205
Email: sami.biz.email@gmail.com
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